Tans barely protect bare buns from sunburns
My kindergartner’s nose and cheeks are currently in bloom with freckles, thanks to spending more time out in the sun as temperatures rise and the days get longer. What little melanin is in her skin is trying its best to absorb ultraviolet radiation (UV) from the sun, but it’s uneven and thus, spotty. Fortunately, instead of just freckles, people with slightly darker skin have more melanocytes to create a more even distribution of melainin, protecting you pretty well from sun damage …right?
A recent study of suntanned butt cheeks have found that a tan doesn’t really provide much protection from UV damage. Butts were used since that skin doesn’t often get much sun exposure, and could start as a blank slate, as far as melanin goes. After carefully getting tanned with small doses of UVA and UVB radiation, the skin was found to only add up to SPF 2 or 3, depending on the starting coloration of the butt. That means that if you normally start to burn in 10 minutes of exposure, a starting tan would only buy you 20-30 minutes more. Helpful, yes, but not really a licence to skip the sunscreen if you’ll be outside for a day, as many people seem to believe.
The concern over this misconception is even stronger if you try to establish your tan with a tanning bed. Tanning beds primarily use UVA light, your body has a harder time protecting itself from as far as long-term damage goes. In the short term, the radiation penetrates more deeply into your skin, giving you a darker color for longer, but gains you none of the more protective elements triggered by UVB exposure. This means your dark tan doesn’t come with the skin thickening, extra melanin, or DNA damage repair that would help make it more useful, and as such you’re left with an even smaller boost to your natural SPF.
My kindergartner said: Butts! She then wanted to confirm if she needed to put sunscreen on her butt, but I’m pretty sure that was just because it was an excuse to say the word “butt” a few more times.
Source: Fact or Fiction?: A "Base Tan" Can Protect against Sunburn by Dina Fine Maron, Scientific American