Skin & the Tanning Process
The process of developing a suntan is actually the body’s natural mechanism for protecting the skin from overexposure to the sun’s ultraviolet rays. To understand this process, one must first understand the structure of human skin. Anatomically, the skin has three primary layers:
- Epidermis: outer/surface skin; has several layers
- Dermis: also called the corium or “true skin”
- Subcutaneous: composed of fatty tissue
Epidermis
Including all of its cell layers, the epidermis is not much thicker than a typical sheet of paper and is the layer of skin where a suntan develops. It is also the layer where sunburn occurs. It begins with the basal, or germinative layer, in which new skin cells originate. In this layer are special cells called melanocytes. When these cells are stimulated by UVB light, they utilize an amino acid in the skin called tyrosine, to produce the pigment, melanin.
UVA light, alone, is not very efficient in stimulating melanin production in the skin. Therefore, the majority of indoor tanning systems in the U.S. utilize lamps with an output combination of UVA and UVB – minimal amounts of UVB to stimulate melanin and UVA sufficient to effectively oxidize or “brown” the melanin.
Melanocytes exposed to UVA/UVB harden on the surface or “horny” layer where they eventually disappear through exfoliation. In this way then, the melanin pigment protects the UVA-sensitive DNA located inside the cell nuclei without obstructing other positive effects of UV light. These cells are shed by the body approximately every 30 days, which is why a tan will fade naturally over time.
Melanin is the leading factor that determines a person’s natural skin color, and its presence is determined by hereditary factors. All people have roughly the same amount of melanocytes, but our bodies produce a certain amount of melanin based on heredity, which is why people of different ethnicities have different skin tones. Also, in darker skin types, the pigment grains are larger and more uniformly distributed throughout the epidermis than in people with lighter skin. Constitutive skin color is related to your hereditary skin type, while facultative skin color, referred to as a “tan,” is the result of deliberate exposure to ultraviolet light. Here, hormonal factors determine the shade of a tan one will develop.
Prolonged tanning and UV overexposure may lead to acanthuses, or severe thickening of the skin’s top layer, which may create a “leathery” look. Tanners should be educated about the “tanning plateau” which is a level during a tanner’s schedule of sessions when they perceive that they are not getting any darker. While certain indoor tanning lotions may increase the appearance of darkening, tanners cannot achieve levels greater than their hereditary skin type determines.
Dermis
This layer could be termed the skin’s “support system” and is the thickest layer. It varies from 1-5 millimeters in thickness and composed mainly of fibers and water. The majority of the fibers (70%) are collagen, which is a connective tissue that gives skin its strength and flexibility. Other fibers present are elastin fibers, which give skin its elastic (“stretchable”) properties. Also present are sudoriferous (sweat) glands and sebaceous (oil) glands, along with blood and lymph vessels, hair follicles and shafts, some fat cells, and nerve fibers providing motor and sensory functions.
UVA can penetrate as far as the dermis layer, while UVB does not. As previously mentioned, long-term overexposure to UVA can cause permanent damage to delicate elastic and connective fibers present in the skin. This is known as elastosis.
Subcutaneous
This skin layer contains fatty and resilient elements, and varies in thickness over different areas of the body. It acts as a cushion for underlying tissue while providing insulation from extremes of hot and cold. This skin layer plays no active role in the tanning process. Ultraviolet light lacks energy sufficient to penetrate past this layer, nor can it reach any internal organs. UV light waves are not microwaves, and – c contrary to myth – you cannot “microwave” the human body in a sunbed.
Summary of the Tanning Process
Most sunbeds emit minimal amounts of UVB to stimulate melanin and effective amounts of UVA to oxidize or “brown” the melanin. So, when the skin is exposed to UVB, melanin cells are produced in the germ, or basal skin layer. These cells migrate toward the surface of the skin, and when exposed to UVA, they are oxidized, giving the appearance of a suntan.
