Friday, July 28, 2006

Black skin, SPF, and when a feature becomes a bug

[Update 7/31: read the comments. The BBC article really mangled the study, and my imagination was overly active. As our commentator notes, these melanomas aren't even clearly sun related. Detection was also not a problem, the involved skin is pale. I really don't know what to make of any of this, but you probably shouldn't waste your time on this post!]

Very black skin has SPF 13; I assume that very pale skin has SPF 1-2 (the BBC article didn't say) ...
BBC NEWS | Health | Dark skin 'does not block cancer'

...people with dark skin are more likely to die from skin cancer than those with fairer skin...

Dark skin has increased epidermal melanin which provides a natural skin protection factor (SPF) - a measure of how long skin covered with sunscreen takes to burn compared with uncovered skin.

Very dark, black skin has a natural SPF of about 13 and filters twice as much UV radiation as white skin, for example.
The BBC article is pretty weak. We're talking about melanoma. Very black skin is protective against melanoma, but it also makes it harder to spot early melanoma. The detection impact is only relevant when melanoma can be treated -- a modern phenomena.

In low tech societies black skin protects against death by melanoma, in high tech societies we can cure early melanoma. So the detection problmes mean that black skin has gone from being a 'feature' to a 'bug' -- at least in terms of melanoma protection. It's still a feature in terms of protection against sunburn, even the best sunscreens require frequent reapplication.

This is analogous to climate change and fur color. White fur is protective when there's snow, a problem when the snow melts. The difference is that our environment is technological.

Asians and other brown skinned persons may have the best compromise here. A reasonable SPF protection (maybe 8?) with reasonably easy detection as well. Sunscreen there just improves the odds. Good news for my younger kids. Getting black kids and adults to wear sunscreen will be damn hard. An effective SPF 13 sunscreen that doesn't wash is good enough to avoid a lot of sunburn, and without the scourge of sunburn kids and adults aren't going to put sunscreen on...

1 comment:

JGF said...

I dug out another article, which showed you are right: "There's usually a delay in diagnosis because they (warning signs) occur in atypical locations in skin of color ..."

Which makes the author's recommendation to use sunscreen even more odd, as you point out the melanomas don't seem to be sun related at all.

Well, so much for that post. I'm quite confused.