Sunblock, Skin Cancer, Evidence Based Medicine, and the Surgeon General

2014 July 30
by Daniel Lakeland

A friend of mine posted a link to news articles about a recent Surgeon General warning about sunscreen

http://www.cnn.com/2014/07/29/health/surgeon-general-skin-cancer/

Quoting from that article:

Skin cancer is on the rise, according to the American Cancer Society, with more cases diagnosed annually than breast, prostate, lung and colon cancer cases combined.

On Tuesday, the United States surgeon general issued a call to action to prevent the disease, calling it a major public health problem that requires immediate action. Nearly 5 million people are treated for skin cancer each year.

But let's dissect this a little bit. First of all, most skin cancer is unlikely to really hurt you. It's melanoma that is the real concern.

cancer.gov gives melanoma rates according to the following graph:

Melanoma diagnosis and death rates through time from seer.cancer.gov

Melanoma diagnosis and death rates through time from seer.cancer.gov

As for melanoma itself, clearly the diagnosed cases are on the rise, but look at the deaths per year. Totally flat. This is consistent with improved diagnosis procedures without any change in actual incidence in the population. Furthermore looking deeper on the melanoma site we see that 5 year survival rates have increased from 82% in 1975 to 93% in 2006, this is also consistent with earlier diagnosis (so that the 5 year rate measures from an earlier point relative to the initiation of the melanoma).

How about melanoma by state? Climate should be involved right? More sun exposure should mean more melanoma?

 

Melanoma rates by state from seer.cancer.gov

Melanoma rates by state from seer.cancer.gov

As you can see, states in the southwest have lower rates, and states in the northwest and northeast have higher rates. The cluster of southeastern states with high rates are interesting too.

Vitamin D is suspected to be involved in several health affects related to cancer, so overall exposure to sun may be beneficial. However, I think that the data is also clear that intense exposure to sun from tanning beds, intentional tanning, and repeated sunburn is bad for your skin.

Sun exposure, like other exposures such as alcohol, may have nonlinear risk effects. At moderate exposures you are better off than at zero exposure (in Oregon rain or Maine winters) or heavy exposure (leading to repeated sunburn and high melanoma risk).

So, is the advice to slather on sunscreen good? I don't think the conclusion is so clear cut, but I don't have any in-depth study data to go on either. All I can tell you is that I'll continue to avoid getting sunburn by covering up and using zinc based sunblock when I'm outside for long periods, but I'll continue to get regular sun exposure without sunblock in mornings, evenings, and mid day during non-summer months.

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