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What Are Ingrown Hairs?

Ingrown Hairs Occur When Shaved or Removed Hairs Get Trapped Inside the Skin, Causing Acne-like Lesions

By: Dan Kern, Acne.org Founder & CSO
Last updated: May 15, 2019

The Essential Information

Ingrown hairs are a common skin condition caused by hair removal in both males and females. They occur when shaved or removed hairs get trapped inside the skin, causing lesions that look like acne but are not actually acne. Ingrown hairs are more common in people with curly hair, especially black males, and can be prevented by stopping or changing hair removal practices. Ingrown hairs may also be treated with a skincare regimen.

The Science

Pseudofolliculitis Barbae

The medical term for "ingrown hairs" is pseudofolliculitis barbae. Hair removal practices which can cause it include:

  • Shaving
  • Waxing
  • Plucking
  • Threading

Ingrown hairs result in firm skin-colored or red or dark acne-like lesions that can be itchy or sore. When they are caused by shaving, they are sometimes called "razor bumps" or "shave bumps."1 Sometimes, these lesions can fill with liquid that resembles pus in some acne lesions.1 Although these breakouts appear similar to acne, they should not be mistaken for it.

Who Is Most Likely to Develop Ingrown Hairs?

Although anyone can develop an ingrown hair from time to time, ingrown hairs are most common in people whose hair curls tightly. Since people of African descent typically have curly hair, they are more prone to developing ingrown hairs than people of European descent. Because of this, black men who shave facial hair are much more likely to develop them than white men who shave facial hair. As Drs. Beth and Adam Goldstein--both professors of medicine at the University of North Carolina--wrote on a website for doctors called UpToDate, "Between 45 and 83 percent of black men and 3 percent of white men who shave facial hair develop [a problem with ingrown hairs]."1 Most people will develop an ingrown hair from time to time--regardless of ethnicity--including women who remove hair. Ingrown hairs most often appear on the cheeks and front of the neck. However, any area of the body where a person removes hair, such as the legs, armpits, or pubic region, can develop them.1

How Do Ingrown Hairs Develop?

When a hair is shaved off or removed by plucking or waxing, it soon begins to regrow but may become trapped in the skin. If the hair gets trapped, the body sees its own hair as an "intruder" and attacks it with an inflammatory response. An inflammatory response is the body's reaction to any foreign object or anything that happens to be in a place on the body where it normally is not supposed to be. When this occurs, the body tries to ward off the "intruder" by attacking it with inflammatory cells and substances. This defensive reaction causes the typical signs of inflammation, such as redness, swelling, heat, and soreness. You can see this reaction when you harm the skin with a wooden splinter and do not remove it immediately: after a while, the skin displays characteristics of inflammation mentioned above.

Normally, hair grows from a hair follicle (sac) and emerges through a pore in the skin. However, when a shaved, plucked, or waxed hair regrows, it can pierce the skin and begin growing in that direction. This can occur in one of two ways.

  1. In extrafollicular penetration, the hair emerges from the skin pore, but then curls back on itself and re-enters the skin near the follicle. In other words, a loop of hair is formed above the skin. This is especially likely to occur when the hair is curly, short, and has a sharp end due to shaving. As the hair continues to grow, it eventually finds its way out of the skin again, but this can take several weeks.1

    Ingrown Hair Extrafollicular Penetration
     
  2. In transfollicular penetration, instead of emerging from the skin pore, the hair pierces the wall of the hair follicle and grows into the surrounding skin. That is to say, there is no loop rising above the skin surface. Rather, the hair remains inside the skin, but instead of growing directly through the pore and out of the skin, it becomes trapped. The hair may continue to grow several millimeters through the dermis, the middle layer of skin, before finding its way out. This typically takes three to six weeks. Just like in extrafollicular penetration, transfollicular penetration is more likely to occur if the hair is curly and has a sharp end.

    Ingrown Hair Transfollicular Penetration

    Transfollicular penetration can also result from stretching the skin when shaving. When a person stretches an area of skin, passes over it with a razor, and then lets go of the skin, the cut hairs shrink back into their follicles. This results in short, sharp-ended hairs just under the skin surface, and these hairs are especially likely to take the wrong path when they start to regrow.

    Multi-blade razors contribute to transfollicular penetration in a similar manner. When a person shaves with a multi-blade razor, the first razor edge pulls the hairs upward and the next razor edge cuts the hairs. After shaving, the hairs shrink back into their follicles. This results in short hairs with sharp ends just beneath the skin surface. Such hairs are likely to grow into the surrounding skin, instead of through the pore.1

People with tightly curled hair, such as people of African descent, are particularly likely to develop ingrown hairs for two reasons.

  1. Tightly curled hair is more likely to curve back toward the surface of the skin.
  2. Hair follicles in people with tightly curled hair are usually angled obliquely to the skin surface, meaning that instead of the hair emerging at a 90-degree angle to the skin surface, the hair comes out at a slant. This angle makes it more likely that a close shave will create hairs with sharp, rather than blunt, edges.1

Ingrown Hairs Are More Common in People with Tightly Curled Hair

Once a regrowing hair pierces the skin by either extrafollicular or transfollicular penetration, the spot where the hair is trapped becomes inflamed, and a dense, flesh-colored or red or hyperpigmented (darker than the surrounding skin) papule appears.1,2 Soon, a pustule (a fluid-filled lesion) may form at the site of the ingrown hair. In contrast to acne pustules, which are filled with pus and bacteria, pustules due to ingrown hairs are often sterile, meaning they are not filled with pus or bacteria. Instead, these pustules contain liquid that comes from the blood vessels near the ingrown hair, which leak liquid into the area. The blood vessels around the hair also swell, causing the skin to become red and warm to the touch. However, scratching or picking at ingrown hairs can cause an open wound--even if that open wound is merely a tiny crack in the skin--which can let bacteria into the skin and lead to infection. If this occurs, pustules containing bacteria and pus may develop, just like in acne.1

Hyperpigmentation after an ingrown hair heals

After the lesion caused by an ingrown hair clears up, the skin can remain hyperpigmented for several months before fading. This is especially likely to occur in dark-skinned people.1

Hyperpigmentation after an Ingrown Hair Heals

Prevention and Treatment

Management of ingrown hairs should be focused on prevention, rather than treatment. Additionally, some topical medications are available to treat ingrown hairs. There are three possible approaches to preventing ingrown hairs.

  1. Stopping hair removal
  2. Employing alternative hair removal practices
  3. Trying long-term hair reduction

Stopping hair removal can eliminate ingrown hairs, while altered hair removal practices usually reduce the number of ingrown hairs that occur. Long-term hair reduction is the "nuclear option" when it comes to ingrown hairs, and can eliminate the need for shaving, plucking, waxing, or threading, and can therefore be a permanent solution to ingrown hairs.1

Ingrown Hair Prevention and Treatment Stopping Hair Removal

Stopping hair removal

Discontinuing shaving, waxing, plucking, and/or threading, and allowing the hair to remain at a length that makes penetration of the skin unlikely is the most effective preventative measure against ingrown hairs. For men, grooming the beard with scissors or an electric clipper can be an alternative to shaving. It is recommended not to cut the hair shorter than 0.5cm (5mm), at least until ingrown hairs clear up. Depending on the person and the severity of the condition, ingrown hairs and any associated hyperpigmentation can take from one to six months to resolve.1

Ingrown Hair Prevention and Treatment Proper Shaving

Alternative hair removal practices

Sometimes, discontinuing hair removal is undesirable or even impossible, such as for men in the U.S. Army and Marine Corps, who are not permitted to grow beards. If you continue to shave, you may want to adjust your shaving routine by following these tips: 

  • Soften the hair before shaving by shaving at the end of a shower, using a highly lubricating shaving cream, and/or applying a shave oil under shaving cream.
  • Use only a one- or two-blade, low-irritation razor and avoid the multi-blade razors.
  • Shave exclusively in the direction of hair growth, which is normally downward on the face and the top half of the neck and upward on the bottom half of the neck.
  • Avoid stretching the skin during shaving.
  • If you do have an ingrown hair, be careful when you shave over it. Shave gently, using only the necessary amount of pressure possible with the razor.

Alternatively, razor blades can be replaced by electric clippers that leave the hair at least 5mm long so that the hair does not curl back and pierce the skin.

Ingrown Hair Prevention and Treatment Laser Hair Removal

Long-term hair reduction

The problem of recurring ingrown hairs can be solved by long-term hair reduction, which destroys the hair follicles. Of course, the downside is that a person can no longer grow hair in that area--for example, a man who undergoes long-term reduction of facial hair will no longer be able to grow a beard. Long-term hair reduction can be accomplished by laser hair removal. It usually requires several sessions in order to achieve a major reduction in hair growth, because each treatment only destroys a small fraction of hair follicles. The lasers work by targeting the dark pigment called melanin, which can be found in both skin and hair. Laser hair removal is most effective when a person's hair contains more melanin, i.e., is darker than, the skin. The laser can then safely destroy the hair follicles without damaging the pigment in the skin. Conversely, the treatment does not work well for people with blond or gray hair because their skin is as dark as, or sometimes even darker than, the hair. Drs. Beth and Adam Goldstein wrote, "[P]atients with darkly pigmented hairs are the best candidates for this procedure. The treatment is poorly effective for white or [gray] hairs."1 Potential risks of laser hair removal include temporary or permanent changes in skin pigmentation, blistering, and scarring. The risk of changes in skin pigmentation is higher for individuals with darker skin. To minimize the chances of this side effect, the clinician should perform a spot test on an area of the skin that is hardly visible, so that he or she can adjust the laser settings prior to treatment.1

Ingrown Hair Prevention and Treatment Topical Medicinal Treatments for Ingrown Hairs

Topical medicinal treatments for ingrown hairs

The most common drugs used to treat ingrown hairs are: 

  • Benzoyl peroxide, especially when combined with alpha hydroxy acids
  • Topical retinoids
  • Low-potency topical corticosteroids
  • Topical antimicrobials, such as erythromycin and clindamycin1

Information on the efficacy of these treatments is limited, and more research is needed to determine how helpful these and other drugs may be in treating ingrown hairs.1

In Conclusion

Both males and females sometimes experience ingrown hairs after hair removal. The lesions that they cause resemble acne and arise due to the hairs growing into surrounding skin, rather than out the pore. There is a correlation between having curly hair and developing ingrown hairs after shaving, as is often the case in black males. Ingrown hairs can be prevented by ceasing or altering hair removal practices but may also be treated with skincare products.

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References:

  1. Goldstein, B. & Goldstein, A. Pseudofolliculitis barbae. (2017). <https://www.uptodate.com/contents/pseudofolliculitis-barbae>.
  2. Oakley, A. Folliculitis barbae and pseudofolliculitis barbae, <https://www.dermnetnz.org/topics/folliculitis-barbae/> (2016).

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