Q: I heard a story on WCMH/Channel 4 recently that HPV causes skin cancer. Is this true?
Short A: Maybe. We don’t really know.
Long A: We know that there is a cause and effect relationship between certain strains of the Human Papilloma Virus (HPV) and cervical and anal cancers. A recent study published in the British Medical Journal suggests there might also be an association between HPV and squamous cell carcinomas (SCC) of the skin. Scientists measured HPV levels in patients who didn’t have SCC and compared them to those who did. They found that patients had a 44% chance of having SCC if they had 2 or 3 strains of HPV; a 51% chance if they had 4 to 8 strains; and a 71% chance if they had more than 8 strains.
But while those numbers look scary, they say nothing about whether HPV causes SCC or not. They imply that there is a correlation between the two conditions, but correlation does not equal causation. HPV and SCC occur together in a lot of people, but maybe having SCC makes some people more susceptible to getting HPV rather than the other way around? You could just as easily say, “The more people you see on the oval carrying umbrellas, the more likely it is to be raining.” But that doesn’t prove that the umbrellas caused the rain.
Here’s another good example of scary numbers, this time from the World Health Organization:
“The use of sunbeds before the age of 35 is associated with a 75% increase in the risk of melanoma”.
So if you’ve ever used a tanning bed, you have a 75% chance of getting melanoma!? No. That number is the relative risk. The absolute risk of getting melanoma from tanning beds is actually very small: less than 0.003% of people who tan frequently get melanoma, compared to less than 0.002% of people who don’t. While that rate is 75% higher, we’re still talking about a very small number – less than 3 out of 1000. There’s a great article explaining all of this stuff over at the Association of Health Care Journalists website.
I’m NOT saying tanning beds are safe. Melanoma is bad and even though it doesn’t happen that often, anything that increases your risk of it even a tiny bit should be avoided. You should wear sunscreen and condoms as often as possible (well, you know, when appropriate… and maybe not at the same time… you know what I mean). My point is that numbers can say very different things depending on how you look at them, and people will often exploit that fact to sell you stuff from milk to medicines, and not always with your best interests at heart.
Being an informed and knowledgeable health care consumer is as important to your health as sunscreen and condoms. So lather up, cover up and always read the fine print. You’ll be glad you did.
Victoria Rentel, MD
Student Health Services
The Ohio State University