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Does sebum help "moisturize" the skin??

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#21 Adri Chan

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Posted 18 April 2008 - 11:02 AM

Accutane will not reduce your sebum on the long term, in fact it's the total opposite, the reason I have seborrheic dermatitis now is because I took that shit, a low carb diet reduces oily skin and I think balance hormones could get rid of it.

Visit this link before ever thinking of taking accutane :

http://www.xsorbit1....avec//index.cgi

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#22 Genius/GZA

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Posted 23 April 2008 - 06:00 PM

Hahahaha eusa_clap.gif
I don't use anything except Jojoba oil to moisturize at night.

#23 jilla

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Posted 17 December 2008 - 07:16 AM

Hey, why do you think it is said that people whose skin produce more sebum age slower? Don't you think sebum has antiwrinkle properties? Think about the lips, palms, soles witch are known not to produce any sebum, and how wrinkled they are in compare to the rest of the body. It seems to me that sebum has a good purpose. I know I'm off topic.
If excess sebum doesn't moisturize the skin so are all the oils? Sebum is oil right?

#24 bryan

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Posted 17 December 2008 - 02:38 PM

QUOTE (jilla @ Dec 17 2008, 07:16 AM) <{POST_SNAPBACK}>
Hey, why do you think it is said that people whose skin produce more sebum age slower? Don't you think sebum has antiwrinkle properties?


Hmmm.... No, not to my knowledge.

QUOTE (jilla @ Dec 17 2008, 07:16 AM) <{POST_SNAPBACK}>
Think about the lips, palms, soles witch are known not to produce any sebum, and how wrinkled they are in compare to the rest of the body.


I don't think they're "wrinkled". There are certainly LINES in them, some of them quite pronounced, but those aren't wrinkles. Look at the underside of each of your 10 fingers, where the fingerprints are. Do you see any "wrinkles" there, or just fingerprints?

QUOTE (jilla @ Dec 17 2008, 07:16 AM) <{POST_SNAPBACK}>
If excess sebum doesn't moisturize the skin so are all the oils? Sebum is oil right?


I think the bottom-line to all this is that theoretically sebum might have a tendency to "moisturize" the skin slightly, but it's such a minor effect that it's of no practical significance.

.

#25 jilla

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Posted 18 December 2008 - 06:33 AM

Does this mean that all the commercial moisturizers are ineffective at hydrating the skin? Because sebum contains almost the same ingredients, except the preservatives; squalene one of the components of sebum has anti-carcinogenic properties and protects the skin from ultraviolet rays thus becoming great in fighting against ageing symptoms.

http://portalmarket.com/shark.html

If you look at the older peoples hands you can see that they have in the palms more lines than on the superior part of the hand, more lines than a young person; thus this lines are wrinkles.

#26 bryan

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Posted 18 December 2008 - 04:04 PM

QUOTE (jilla @ Dec 18 2008, 07:33 AM) <{POST_SNAPBACK}>
Does this mean that all the commercial moisturizers are ineffective at hydrating the skin? Because sebum contains almost the same ingredients, except the preservatives;


I think it's probably a matter of quantity: there's not enough sebum around to make that much of a difference, although it might theoretically have a slight moisturizing effect. It's a different matter when you take a commercial moisturizer and smear several drops of it all over your face.

.

#27 Le_Chaim

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Posted 19 December 2008 - 12:00 AM

Very interesting topic....

#28 everyskyisblue__

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Posted 19 December 2008 - 07:31 PM

Sebum may not have moisturizing properties itself, but in amounts that aren't excessive it does help to seal in moisture on skin and hair.

WebMD-Oily Skin Article

Also, my dad, my aunt, and my grandpa all suffer from oily skin and do not have very many wrinkles at all. In fact, my aunt and dad are totally wrinkle free and my grandpa, who is 80, only has a handful of wrinkles.
my regimen.

Morning:
Drink at least a glass of water.
Wash face with Olay Sensitive Skin Foaming Wash or water.
Apply Cetaphil Lotion.

Night:
Take Ortho Tri-Cyclin
Remove makeup with wipes.
Wash face with Olay.

Status: 90% clear of active acne. I just stopped giving a crap and got on a good birth control. Your skin can work itself out 80% of the time and nothing you put ON it is going to help forever. Your skin doesn't work like that. Topical stuff just delays skin's problems or makes them stop temporarily. You have to stop trying so damn hard to control your skin and, if that doesn't work, you probably need Accutane or something else to correct the INTERNAL cause of your external problem.

#29 adamrodriguez

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Posted 21 December 2008 - 05:44 AM

well id rather have wrinkles when im old rather than excessive oiliness in my young years.
How To Wash Your Face The Right Way

Product Ingredients To Avoid

Why Moisturizer Is Important

products I currently use:
L'Bri Pure N Natural Deep Pore Cleanser & Oil-Free Moisturizer
Forever Living Products "Aloe Vera Gelly" Moisturizer

#30 everyskyisblue__

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Posted 21 December 2008 - 01:54 PM

Well, I'd rather look good my entire life.

I want to go to my 30 year high school reunion and laugh at all the bitches that look like leather handbags while my face is still practically wrinkle free thanks to my oily skin genes.

Oily skin is not a social death sentence. It just means you have to blot a few times a day. Big effing deal.
my regimen.

Morning:
Drink at least a glass of water.
Wash face with Olay Sensitive Skin Foaming Wash or water.
Apply Cetaphil Lotion.

Night:
Take Ortho Tri-Cyclin
Remove makeup with wipes.
Wash face with Olay.

Status: 90% clear of active acne. I just stopped giving a crap and got on a good birth control. Your skin can work itself out 80% of the time and nothing you put ON it is going to help forever. Your skin doesn't work like that. Topical stuff just delays skin's problems or makes them stop temporarily. You have to stop trying so damn hard to control your skin and, if that doesn't work, you probably need Accutane or something else to correct the INTERNAL cause of your external problem.

#31 bryan

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Posted 13 February 2009 - 02:17 AM

I'm BUMPING this thread for all the new posters to see! eusa_angel.gif

#32 tygerskyn

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Posted 13 February 2009 - 02:42 AM

I saw a post that caught my attention, asking if jojoba oil or emu oil are redundant if sebum does not moisturize the skin.

I don't think they are redundant, since there is a theory that they "trick" the skin into thinking it is producing more sebum than it actually is, but they are not as prone to create blocked pores as actual sebum is.

So please correct me if I'm wrong, but the jojoba/emu oil could assist in clearing up skin because they help discourage sebum production?
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#33 bryan

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Posted 13 February 2009 - 03:17 AM

QUOTE (tygerskyn @ Feb 13 2009, 03:42 AM) <{POST_SNAPBACK}>
I saw a post that caught my attention, asking if jojoba oil or emu oil are redundant if sebum does not moisturize the skin.


I think jojoba and emu oils are MUCH more likely to "moisturize" the skin than sebum, for the simple reason that they are applied in FAR higher quantities than sebum.

QUOTE (tygerskyn @ Feb 13 2009, 03:42 AM) <{POST_SNAPBACK}>
I don't think they are redundant, since there is a theory that they "trick" the skin into thinking it is producing more sebum than it actually is, but they are not as prone to create blocked pores as actual sebum is.

So please correct me if I'm wrong, but the jojoba/emu oil could assist in clearing up skin because they help discourage sebum production?


<groan>

The skin doesn't know and doesn't care about the presence or absence of sebum. The sebaceous glands just keep doing their thing, producing oil at a relatively steady clip, regardless of the presence or absence of oil on the surface (although the glands are indeed influenced by certain hormones and drugs). Therefore, you can't "trick" the sebaceous glands into producing less sebum by such a simplistic method, unless the oil that you apply has some kind of drug or hormone in it which can seep down into the sebaceous glands and alter their metabolism directly.

#34 tygerskyn

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Posted 13 February 2009 - 05:15 PM

QUOTE (bryan @ Feb 13 2009, 03:17 AM) <{POST_SNAPBACK}>
QUOTE (tygerskyn @ Feb 13 2009, 03:42 AM) <{POST_SNAPBACK}>
I saw a post that caught my attention, asking if jojoba oil or emu oil are redundant if sebum does not moisturize the skin.


I think jojoba and emu oils are MUCH more likely to "moisturize" the skin than sebum, for the simple reason that they are applied in FAR higher quantities than sebum.

QUOTE (tygerskyn @ Feb 13 2009, 03:42 AM) <{POST_SNAPBACK}>
I don't think they are redundant, since there is a theory that they "trick" the skin into thinking it is producing more sebum than it actually is, but they are not as prone to create blocked pores as actual sebum is.

So please correct me if I'm wrong, but the jojoba/emu oil could assist in clearing up skin because they help discourage sebum production?


<groan>

The skin doesn't know and doesn't care about the presence or absence of sebum. The sebaceous glands just keep doing their thing, producing oil at a relatively steady clip, regardless of the presence or absence of oil on the surface (although the glands are indeed influenced by certain hormones and drugs). Therefore, you can't "trick" the sebaceous glands into producing less sebum by such a simplistic method, unless the oil that you apply has some kind of drug or hormone in it which can seep down into the sebaceous glands and alter their metabolism directly.


Ah, it's kind of hard to wrap my brain around the idea that the sebum glands aren't influenced by things you put on your skin. It just seems like the entire body is always striving for equilibrium, constantly reacting to its environment.

I guess I just don't understand why they would keep producing oil regardless. It seems like they wouldn't be there at all if they did not serve any purpose, and also weren't affected by our environment.
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#35 bryan

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Posted 13 February 2009 - 06:01 PM

QUOTE (tygerskyn @ Feb 13 2009, 05:15 PM) <{POST_SNAPBACK}>
Ah, it's kind of hard to wrap my brain around the idea that the sebum glands aren't influenced by things you put on your skin.


Huh?? The sebum glands _are_ influenced by certain things you can put on your skin, just not certain OTHER things that posters on this forum are accustomed to talking about! smile.gif

Washing the skin doesn't influence them, but a small amount of GLA (gamma-linolenic acid, a fatty acid) applied to human skin has been shown to reduce sebum production, presumably because of its ability to inhibit 5a-reductase and even interfere with androgen receptors; similarly, topical 17a-propylmesterolone and other antiandrogens have also been shown to reduce sebum production to some extent. So it's possible to find topical agents which can do the job, you just have to know which ones to try.

QUOTE (tygerskyn @ Feb 13 2009, 05:15 PM) <{POST_SNAPBACK}>
I guess I just don't understand why they would keep producing oil regardless. It seems like they wouldn't be there at all if they did not serve any purpose, and also weren't affected by our environment.


It's still relatively early in our evolutionary history. I suspect they're on their way out.

#36 tygerskyn

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Posted 14 February 2009 - 07:02 AM

Thank you for this information, I'm glad to keep learning what I can about my skin.
Click Here for my Topical Retinoid blog.

#37 toomuchaccutane

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Posted 24 October 2009 - 06:02 PM

QUOTE (bryan @ Dec 17 2008, 02:38 PM) <{POST_SNAPBACK}>
QUOTE (jilla @ Dec 17 2008, 07:16 AM) <{POST_SNAPBACK}>
Hey, why do you think it is said that people whose skin produce more sebum age slower? Don't you think sebum has antiwrinkle properties?


Hmmm.... No, not to my knowledge.

QUOTE (jilla @ Dec 17 2008, 07:16 AM) <{POST_SNAPBACK}>
Think about the lips, palms, soles witch are known not to produce any sebum, and how wrinkled they are in compare to the rest of the body.


I don't think they're "wrinkled". There are certainly LINES in them, some of them quite pronounced, but those aren't wrinkles. Look at the underside of each of your 10 fingers, where the fingerprints are. Do you see any "wrinkles" there, or just fingerprints?

QUOTE (jilla @ Dec 17 2008, 07:16 AM) <{POST_SNAPBACK}>
If excess sebum doesn't moisturize the skin so are all the oils? Sebum is oil right?


I think the bottom-line to all this is that theoretically sebum might have a tendency to "moisturize" the skin slightly, but it's such a minor effect that it's of no practical significance.

.

If you say theoretically that sebum moisturizes the skin slightly, should i be upset that accutane has completely shrunk my sebaceous glands and i no longer have any surface sebum on my skin? Won't i start to age quicker, and wrinkles will become more obvious without sebum?


#38 Heartless

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Posted 24 October 2009 - 07:29 PM

Oil (in this case, in the form of sebum) and moisturization are two different concepts. Moisturization is introducing hydration (e.g. water) into the skin. However, as we all know, water evaporates quite quickly from the skin's surface and the environment will cause the water within the skin to dry out, too. Oil or lipids act as lubrication or protection for the skin by trapping the water molecules within the skin and keeping it from evaporating as quickly.

Example: skin care experts advise putting a thin layer of body oil over your skin after towel drying yourself following a shower. The purpose is to trap the hydration from the water molecules in the skin.

Bottom line: "Moisturizers" provide a balance between infusing the skin with hydration and applying a thin layer of protection to keep that hydration along with other so-called "beneficial ingredients" within the skin. So, yes, people with oily skin will still see wrinkles over time because of the skin's loss of hydration.




#39 bryan

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Posted 21 November 2009 - 01:20 PM

Below is a rather extended excerpt from the same article I referenced in the first post in this thread: "The Uses of Sebum", by Albert M Kligman MD, Phd. The whole article is quite long and involved, so I only had time to copy some of his comments about the (alleged) effects of sebum as a "moisurizing" agent. What I found particularly fascinating is his description of the experiment near the end, showing that it takes FAR more sebum than is normally present on the skin of a human (10-20 times as much) before the amount of water loss even BEGINS to be diminished just a bit! smile.gif

QUOTE
The lipid film.--The surface lipids form a film whose thickness has been estimated to be 3-10 um (Miescher and Schonberg, 1944). We must know the physical structure of this film, if it is to reveal its numerous protective roles.

For emphasis let us calculate the thickness of the film on the forehead of a very oily subject whose casual sebum level is 0.4 mg. per sq. cm. The casual level is the fairly constant and maximum amount of oil which the surface supports unless some artificial trap is provided to check the run-off. Assuming a specific gravity of 0.9, the film would be only about 0.45 um (micron) thick. Since the forehead is one of the oiliest regions, let us consider the extremities, the abdomen or most other skin territories with a low density of sebaceous glands. An average casual level for these regions is perhaps 0.05 mg. per sq. cm and a corresponding thickness of about 50 m-um (milli-microns). This puts us squarely in the realm of submicroscopic ultrafilms. Too little attention has been paid to the really trivial quantities of sebum which cover most of the body surface. The large number of important roles assigned to sebum are disproportionate to the miniscule amounts that are actually present.

If one liberally inuncts sebum on to a sheet of isolated stratum corneum (see below) wiping off the excess with the finger but still leaving the surface visibly greasy, the amount deposited is of the order of 0.03 to 0.05 mg. per sq. cm. If the sebum is warmed and literally poured over the surface, shaking off the excess, the amount rises to about 0.5 mg. per sq. cm., corresponding to a film with thickness just about visible in the light microscope. The skin surface does not hold much fat.

Actually, the above calculations of film thickness are inappropriate and misleading. The skin is not a plane surface. It is transected by furrows which carve out intricate patterns in different regions, giving rise to the characteristic skin markings or dermatoglyphics. When one closely observes a freshly defatted area, the sebum droplets that arise in the orifices soon run off into the furrows amd are carried away. Butcher and Parnell (1948) were the first to emphasize that sebum streamed preferentially into the furrows. The speed with which sebum is lost from an unprotected area is responsible for another esteemed myth, the so-called "feed-back" mechanism for controlling sebaceous secretion. As soon as a certain fat level was reached on the surface, the economy-minded glands were supposed to shut down. No such thing happens. Shelley and I have dealt with this appealing fallacy elsewhere (Kligman and Shelley, 1958). The gland secretes continuously.

When one exposes various areas of the skin to osmic acid fumes and examines the disposition of the lipids directly under the skin microscope, with a magnification of 40-80 diameters, it becomes clear that there is often no simple uniform film. In oily areas much of the visible fat is in the form of droplets and rivulets of varying sizes and shapes, principally in the valleys. In low sebum regions, that is, over most of the body, surprisingly little is seen. The lipid is smeared out into submicroscopic films which are too thin to be visualized even with the aid of osmic acid.

In summary, the general surface is smeared with an ultrafilm; in oily regions enough fat may accumulate to form droplets and globules, whose size and shape are continuously changing. The ultrafilm extends into crevices of the outermost cell layers of the stratum corneum. Our previous concept that the whole stratum corneum is porous and acts as a sebum reservoir, like a sponge, is mistaken.

Comparative physiology.--Biologists long ago learned to take advantage of the diversity of species to understand the function of a given structure. The method of comparitive physiology is applicable to the present discussion for there is a curious animal, the prepubertal child, whose sebaceous glands are decidedly undeveloped. This animal has been celebrated by poets and mothers for its smooth, soft, non-greasy skin. Yet, the tiny supply of sebum does not embarrass or compromise the skin of this animal in any way.

The prepubertal subject does have some surface fat. This is derived largely from the epidermis itself, by the steady exfoliation of keratinized cells, giving rise to the so-called horn fat. This source is evidently sufficient for whatever use grease might have on the surface of the skin of man.

No dermatologic condition is known in which only the sebaceous glands are missing or are abnormal. The dryness and scaling associated with genetic ectodermal defects or heavy metal poisoning, for example, cannot be ascribed simply to a lack of sebum. Other profound changes are present, notably abnormalities of sweating and a malfunctioning epidermis. The same is true of aged skin. There is no justification for using such examples to demonstrate the value of sebum. In sum, the prepubertal example is enough to illustrate that skin can be healthy and have charming cosmetic qualities in the virtual absence of sebum.

Surface lipids as adjuncts to the barrier function of skin.--The prime function of skin is protection. One aspect of this is the relatively high impermeablity of skin to water and other substances. This important barrier function resides mainly in the stratum corneum. It should be noted that the horny later is a two-way barrier, preventing equally the ingress and egress of materials. It is a true seal.

In the past the idea was prevalent that the removal of surface lipids facilitated the penetration of water-soluble substances; sebum was supposed to help to keep things out. For example, the treatment of skin with organic solvents such as benzene and alcohol was said to weaken the skin's impermeability to water soluble materials (Calvery, Draize, and Lang, 1946). Yet no quantitative proof was offered. Rothman (1954) thinks the idea has been overdone. Blank and Gould (1961) have removed the surface lipids by pretreating isolated skin for several hours with acetone, ethyl alcohol and ether mixtures. Yet this did not render the skin permeable to sodium dodecyl sulphate. However, when pieces of skin were immersed in such solvents for three days, grossly degrading the tissue, penetration occurred. This seems to be the very point. When used excessively, lipid solvents will increase permeability by disrupting the barrier. Not lipid removal, but injury is the means by which solvents can enhance penetration.

Brun (1952) found that defatting with ether-alcohol intensifies the anhidrosis produced by aluminum chloride. He believes that the sebaceous layer protects the skin against the action of aluminum salts. I repeated this study several times by weighing the quantities of thermogenic sweat retained in cotton pads and was not able to verify this result.

There is a belief that the surface lipids might impede the loss of water to the environment, thus preventing drying out of the horny layer. However, Winsor and Burch (1956) and later Blank (1952) showed that defatting of excised skin had no effect on the rate of water loss. In view of the small quantity of surface lipids, one would hardly expect any other result. Liberal amounts of hydrophobic greases, such as petrolatum, do indeed retard the transpiration of water. Actually the stratum corneum is a remarkably effective water-tight seal comparing favourably with many plastic films of similar thickness (Rosenberg, et al., 1962). The rate of water transpiration of skin both in vitro and in vivo, is of the order of 0.2 - 0.5 mg./cm.^2/hr. for average atmospheric conditions.

It seemed worth while to obtain some quantitative extimate of the effect of adding known amounts of sebum to excised skin using diffraction chamber techniques (Winsor et al., 1956; Blank, 1952). The sebum used was a pooled sample obtained by dipping scalps in a basin of either. The epidermis of fresh abdominal skin was separated by immersion in water at 65 degrees C. for one minute and briefly defatted in ether. The epidermal membranes were kept in the refrigerator until they were mounted on the chamber, after which ether solutions of sebum were evenly spread over the surface. The chambers were kep in a silica gel dessicator at room temperature and weighted daily for four days. Maximum water loss can be expected when the relative humidity is zero. Four pieces of skin were used and the transpiration rate for each specimen was determined for each sebum level, defatting the surface anew for each four-day period.

Table I. -- The Effect of Sebum on the Transpiration of Water.

Sebum Level .......... Transpiration rate of water
(mg/cm^2) ............ (mg/cm^2/hr)
None ...................... 0.71
0.05 ....................... 0.64
0.20 ....................... 0.80
0.61 ....................... 0.73
2.1 ......................... 0.65
3.7 ......................... 0.52

Table I displays the averages for the four samples. It is not until the level approaches 3.5 mg. per sq. cm., at least ten times the average amount found in an oily region, that some modest interference with water loss occurs. Within and well above the normal levels there can be no doubt of the insignificance of sebum as a waterproofing material. Even if the lipid layer were far thicker than it actually is, its effectiveness would be largely minimized by its tendency to flow in the valleys, leaving the major evaporating surface unchanged.

The intricate surface sculpturing of human skin mainly absent in furry animals additionally reduces the water conserving role of sebum.

Edited by bryan, 21 November 2009 - 01:50 PM.


#40 toomuchaccutane

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Posted 23 November 2009 - 11:17 AM

QUOTE (bryan @ Nov 21 2009, 02:20 PM) <{POST_SNAPBACK}>
Below is a rather extended excerpt from the same article I referenced in the first post in this thread: "The Uses of Sebum", by Albert M Kligman MD, Phd. The whole article is quite long and involved, so I only had time to copy some of his comments about the (alleged) effects of sebum as a "moisurizing" agent. What I found particularly fascinating is his description of the experiment near the end, showing that it takes FAR more sebum than is normally present on the skin of a human (10-20 times as much) before the amount of water loss even BEGINS to be diminished just a bit! smile.gif

QUOTE
The lipid film.--The surface lipids form a film whose thickness has been estimated to be 3-10 um (Miescher and Schonberg, 1944). We must know the physical structure of this film, if it is to reveal its numerous protective roles.

For emphasis let us calculate the thickness of the film on the forehead of a very oily subject whose casual sebum level is 0.4 mg. per sq. cm. The casual level is the fairly constant and maximum amount of oil which the surface supports unless some artificial trap is provided to check the run-off. Assuming a specific gravity of 0.9, the film would be only about 0.45 um (micron) thick. Since the forehead is one of the oiliest regions, let us consider the extremities, the abdomen or most other skin territories with a low density of sebaceous glands. An average casual level for these regions is perhaps 0.05 mg. per sq. cm and a corresponding thickness of about 50 m-um (milli-microns). This puts us squarely in the realm of submicroscopic ultrafilms. Too little attention has been paid to the really trivial quantities of sebum which cover most of the body surface. The large number of important roles assigned to sebum are disproportionate to the miniscule amounts that are actually present.

If one liberally inuncts sebum on to a sheet of isolated stratum corneum (see below) wiping off the excess with the finger but still leaving the surface visibly greasy, the amount deposited is of the order of 0.03 to 0.05 mg. per sq. cm. If the sebum is warmed and literally poured over the surface, shaking off the excess, the amount rises to about 0.5 mg. per sq. cm., corresponding to a film with thickness just about visible in the light microscope. The skin surface does not hold much fat.

Actually, the above calculations of film thickness are inappropriate and misleading. The skin is not a plane surface. It is transected by furrows which carve out intricate patterns in different regions, giving rise to the characteristic skin markings or dermatoglyphics. When one closely observes a freshly defatted area, the sebum droplets that arise in the orifices soon run off into the furrows amd are carried away. Butcher and Parnell (1948) were the first to emphasize that sebum streamed preferentially into the furrows. The speed with which sebum is lost from an unprotected area is responsible for another esteemed myth, the so-called "feed-back" mechanism for controlling sebaceous secretion. As soon as a certain fat level was reached on the surface, the economy-minded glands were supposed to shut down. No such thing happens. Shelley and I have dealt with this appealing fallacy elsewhere (Kligman and Shelley, 1958). The gland secretes continuously.

When one exposes various areas of the skin to osmic acid fumes and examines the disposition of the lipids directly under the skin microscope, with a magnification of 40-80 diameters, it becomes clear that there is often no simple uniform film. In oily areas much of the visible fat is in the form of droplets and rivulets of varying sizes and shapes, principally in the valleys. In low sebum regions, that is, over most of the body, surprisingly little is seen. The lipid is smeared out into submicroscopic films which are too thin to be visualized even with the aid of osmic acid.

In summary, the general surface is smeared with an ultrafilm; in oily regions enough fat may accumulate to form droplets and globules, whose size and shape are continuously changing. The ultrafilm extends into crevices of the outermost cell layers of the stratum corneum. Our previous concept that the whole stratum corneum is porous and acts as a sebum reservoir, like a sponge, is mistaken.

Comparative physiology.--Biologists long ago learned to take advantage of the diversity of species to understand the function of a given structure. The method of comparitive physiology is applicable to the present discussion for there is a curious animal, the prepubertal child, whose sebaceous glands are decidedly undeveloped. This animal has been celebrated by poets and mothers for its smooth, soft, non-greasy skin. Yet, the tiny supply of sebum does not embarrass or compromise the skin of this animal in any way.

The prepubertal subject does have some surface fat. This is derived largely from the epidermis itself, by the steady exfoliation of keratinized cells, giving rise to the so-called horn fat. This source is evidently sufficient for whatever use grease might have on the surface of the skin of man.

No dermatologic condition is known in which only the sebaceous glands are missing or are abnormal. The dryness and scaling associated with genetic ectodermal defects or heavy metal poisoning, for example, cannot be ascribed simply to a lack of sebum. Other profound changes are present, notably abnormalities of sweating and a malfunctioning epidermis. The same is true of aged skin. There is no justification for using such examples to demonstrate the value of sebum. In sum, the prepubertal example is enough to illustrate that skin can be healthy and have charming cosmetic qualities in the virtual absence of sebum.

Surface lipids as adjuncts to the barrier function of skin.--The prime function of skin is protection. One aspect of this is the relatively high impermeablity of skin to water and other substances. This important barrier function resides mainly in the stratum corneum. It should be noted that the horny later is a two-way barrier, preventing equally the ingress and egress of materials. It is a true seal.

In the past the idea was prevalent that the removal of surface lipids facilitated the penetration of water-soluble substances; sebum was supposed to help to keep things out. For example, the treatment of skin with organic solvents such as benzene and alcohol was said to weaken the skin's impermeability to water soluble materials (Calvery, Draize, and Lang, 1946). Yet no quantitative proof was offered. Rothman (1954) thinks the idea has been overdone. Blank and Gould (1961) have removed the surface lipids by pretreating isolated skin for several hours with acetone, ethyl alcohol and ether mixtures. Yet this did not render the skin permeable to sodium dodecyl sulphate. However, when pieces of skin were immersed in such solvents for three days, grossly degrading the tissue, penetration occurred. This seems to be the very point. When used excessively, lipid solvents will increase permeability by disrupting the barrier. Not lipid removal, but injury is the means by which solvents can enhance penetration.

Brun (1952) found that defatting with ether-alcohol intensifies the anhidrosis produced by aluminum chloride. He believes that the sebaceous layer protects the skin against the action of aluminum salts. I repeated this study several times by weighing the quantities of thermogenic sweat retained in cotton pads and was not able to verify this result.

There is a belief that the surface lipids might impede the loss of water to the environment, thus preventing drying out of the horny layer. However, Winsor and Burch (1956) and later Blank (1952) showed that defatting of excised skin had no effect on the rate of water loss. In view of the small quantity of surface lipids, one would hardly expect any other result. Liberal amounts of hydrophobic greases, such as petrolatum, do indeed retard the transpiration of water. Actually the stratum corneum is a remarkably effective water-tight seal comparing favourably with many plastic films of similar thickness (Rosenberg, et al., 1962). The rate of water transpiration of skin both in vitro and in vivo, is of the order of 0.2 - 0.5 mg./cm.^2/hr. for average atmospheric conditions.

It seemed worth while to obtain some quantitative extimate of the effect of adding known amounts of sebum to excised skin using diffraction chamber techniques (Winsor et al., 1956; Blank, 1952). The sebum used was a pooled sample obtained by dipping scalps in a basin of either. The epidermis of fresh abdominal skin was separated by immersion in water at 65 degrees C. for one minute and briefly defatted in ether. The epidermal membranes were kept in the refrigerator until they were mounted on the chamber, after which ether solutions of sebum were evenly spread over the surface. The chambers were kep in a silica gel dessicator at room temperature and weighted daily for four days. Maximum water loss can be expected when the relative humidity is zero. Four pieces of skin were used and the transpiration rate for each specimen was determined for each sebum level, defatting the surface anew for each four-day period.

Table I. -- The Effect of Sebum on the Transpiration of Water.

Sebum Level .......... Transpiration rate of water
(mg/cm^2) ............ (mg/cm^2/hr)
None ...................... 0.71
0.05 ....................... 0.64
0.20 ....................... 0.80
0.61 ....................... 0.73
2.1 ......................... 0.65
3.7 ......................... 0.52

Table I displays the averages for the four samples. It is not until the level approaches 3.5 mg. per sq. cm., at least ten times the average amount found in an oily region, that some modest interference with water loss occurs. Within and well above the normal levels there can be no doubt of the insignificance of sebum as a waterproofing material. Even if the lipid layer were far thicker than it actually is, its effectiveness would be largely minimized by its tendency to flow in the valleys, leaving the major evaporating surface unchanged.

The intricate surface sculpturing of human skin mainly absent in furry animals additionally reduces the water conserving role of sebum.



Thanks for posting this Bryan. So, what they are saying is that you would need atleast 10 times the amount of oil on a subject with already very oily skin to make a difference in transpiration of water?

Also, I didn't exactly understand what Kligman's findings were in relation to sebum and its effect on hair. What did he find in that study. The sebum was not needed or it was?