- Basic Structure of Human Skin
- How Do the Lips Differ from the Rest of the Skin, and How Does This Affect Tanning or Burning of the Lips?
- The Effects of Sun Damage on Lips
- Sunburn vs. Suntan of the Lips
- How to Protect Lips from UV Radiation
- The Bottom Line
Basic Structure of Human Skin
Human skin, including the lips, comprises three basic layers:
- The epidermis (the outermost layer)
- The dermis (the middle layer)
- The hypodermis (the bottommost layer)
The sun’s burning and tanning effects take place in the first two layers of the skin: the epidermis and dermis.
How Do the Lips Differ from the Rest of the Skin, and How Does This Affect Tanning or Burning of the Lips?
Little to No Melanin
Melanin is a pigment in the skin that gives skin its color and protects the skin from the sun—the more melanin, the greater skin protection. The lips, however, contain little, if any, melanin. The lips' reddish color instead comes from blood vessels in the dermis, rather than from melanin. The lips' lack of melanin means they are less protected from the sun and more prone to sunburn.1–3
Thinner Skin with No Oil Glands
The skin of the lips is one of the thinnest-skinned areas of the entire body, having a thickness of 1–2mm, and the epidermis is only 0.012–0.7mm thick.
All areas of the skin have a layer of skin cells close to the surface called the stratum corneum, which helps prevent water loss. Compared to skin on the rest of the body, the skin on the lips has a very thin stratum corneum, which means more water can be lost from the lips than from other areas of the skin.
To make matters worse, the lips contain no hair, and therefore no skin oil glands that are attached to hairs, which help lubricate and moisturize the skin.
For all of these reasons, the skin of the lips is more susceptible to the drying effects of sunburn.
The Effects of Sun Damage on Lips
There are three types of radiation generated by the sun that reach the Earth’s surface.
- Ultraviolet (UV)
- Infrared (IR)
- Visible light4
Of these, UV radiation is the type that burns or tans the skin. UV radiation itself is broken down into three categories, according to their wavelengths.
- UVA radiation: Primarily responsible for skin tanning
- UVB radiation: Primarily responsible for skin burning
- UVC radiation: Unable to penetrate the ozone layer and thus does not reach the Earth’s surface5
As shown in the chart below, each type of UV radiation possesses a different wavelength, which limits how far into the skin they can penetrate. UVA radiation has the longest wavelength and UVC, the shortest. Since UVA rays are longer in wavelength, they are able to penetrate deeper into the skin than UVB rays, activating melanin production and tanning the skin. UVB rays do not reach as far down and are almost entirely absorbed by the epidermis. Because UVB rays do not penetrate the skin where melanin is produced, they do not affect tanning as much as UVA rays and are responsible mainly for burning the top of the skin.5,6
Sunburn vs. Suntan of the Lips
Sunburn is an acute inflammatory response of the skin to exposure primarily to UVB radiation and can manifest on any area of the skin, including the lips. UV radiation induces the skin to produce inflammatory molecules, which cause visible redness and swelling. In an attempt to protect itself from damage, skin cells may also begin to divide into more cells, resulting in thickening of the skin within a few hours of sunburn.5
Like sunburn, suntan is a protective measure taken by the skin in response to sun damage. However, suntan is regulated by melanin. The lips contain little to no melanin, so they do not tan. Suntan happens in two phases.
- Phase 1 is the initial pinkening or slight darkening of the skin in reaction to melanin’s exposure to the sun. This is the result of changes to the existing melanin in the skin.
- Phase 2 of suntan occurs later—several hours, or even up to several days, after sun exposure—when the skin appears darker. This results from the skin producing more melanin and is what typically is referred to as “suntan.”5
Because they contain very little or no melanin, the process of sun tanning rarely occurs in the lips, making sunburn their primary type of reaction to sun exposure.
Given the lips’ propensity toward burning, it is important to determine how to protect the lips from sun damage.
How to Protect Lips from UV Radiation
Since sun damage to the lips is similar to sun damage to other areas of the skin, like measures must be taken to protect them as are taken to protect the skin in general. Proper sun protection and limiting sun exposure can significantly lower the incidence of sunburn on the lips. Steps that you can take are:
- Wearing protective hats
- Avoiding outdoor activities when the sun is “highest” in the sky
- Selecting a good sunscreen-containing lip balm or lipstick, with an SPF of at least 15 and that offers broad-spectrum protection
Applying the lip balm or lipstick liberally and reapplying every two hours while in the sun7–11
The Bottom Line
Due to their lack of melanin, the lips are more prone to burn than the rest of the skin, and they rarely tan. Taking proper precautions, such as limiting sun exposure and applying sunscreen, can drastically reduce this risk and is worth making a part of your daily skincare routine.