How Does It Work? Tanning
Although we are only just now beginning to elucidate the mechanisms of tanning, the dramatic increase in melanoma frequencies has made this an important issue of dermatological study. According to the Skin Cancer Foundation, the frequency of melanoma in women has increased 800% since 1970. This startling increase may be at least partially explained by use of tanning beds and by childhood sunburns accrued on family vacations. Now, I think, is the time to curse any loving family members who may have taken you to the beach.
The pigment associated with tanning is called melanin. Melanin absorbs UV light, protecting the skin. Because there are so many different molecular structures for various
melanins, characterizing them has been a challenge for scientists. However, it clear that melanin is capable of absorbing all UV light, and its potential to absorb light decreases exponentially as you get closer and closer to the visible spectrum. Melanin has an estimated SPF of somewhere between 1.5 and 4. (This means that it is able to absorb somewhere 50 and 75% of UV rays). That’s hardly a replacement for sunscreen, but clearly offers some protective effects. Additionally, melanin also may be able to form “caps” on top of the nucleus, reducing DNA damage caused by UV rays.
Melanin in pigmented melanoma
Unfortunately, melanin molecules are hardly an inert guards protecting your skin with diligence. Once exposed to light, they may degrade or produce free radicals. This lessens their effectiveness and may even prove to be damaging.
Merely knowing that melanin is the pigment of a golden tan is remarkably little knowledge. We can easily imagine a variety of ways that UV light could induce darker skin. Hypotheses have included the the stimulation of melanogenesis and changing the shape of the melanin. In the end, a 2005 study published in Nature by Tadokoro and colleagues showed it was neither!
It appears that the main mechanism of action for tanning is the migration of melanin towards the surface of the skin, a process that occurs within one week of UV exposure. Normally, melanin would take closer to four weeks to migrate from the basal layer of skin to the surface.
Although we normally think of UVA light as the rays associated with tanning and UVB light as the rays associated with sunburns, there is evidence suggesting that a secondary tanning mechanism is caused by UVB light: melanogenesis. Indeed, these two mechanisms have been separated out by Miyamura and colleagues. They found that tanning induced by UVA light had no protective effect on DNA damage, but tanning induced by UVB light did have a slight protective effect. Because UVA light merely results in the rearrangement of pre-existing melanin, whereas UVB light stimulates melanin production, only the latter is capable of reducing DNA damage associated with sun exposure.
It is important to note, of course, that all UV exposure causes DNA and other cellular damage, leading to increases risks of skin cancer… so getting a “base tan” in UVB light is hardly an effective method of keeping your skin healthy. Furthermore, if you wanted to get your base tan in a tanning bed, you’d be especially shit out of luck. Tanning beds are 97% UVA, which, as shown in the Miyamura study, is not protective of DNA damage… All that the base tan would give you is a false sense of security.