A healthy living blog from Marshfield Clinic Health System

Getting skin cancer where ‘the sun don’t shine’

Illustration - looking at a foot through a magnifying glassFor years, dermatologists have preached about the virtues of sun screens, for good reason. They work.

However, it’s also true that skin cancer can appear in areas of the body that have no skin exposed to the sun. We’re talking about some mighty private areas as well as seemingly underexposed areas like the palms of the hand and soles of the feet.

How can that be?

While there are three types of skin cancer – basal cell, squamous cell and melanoma – let’s focus on melanoma, the most aggressive and dangerous. Just within that type of cancer, there are two different lines or lineages, both with different reactions to sun exposure.

“Bad sunburns seem to track with one line of melanoma,” said Dr. Erik Stratman, a Marshfield Clinic dermatologist. “Even a single sunburn can increase the risk of that type of melanoma. The other line of melanoma is not directly related to sun and may actually be less likely in sites of chronic, or long term exposure.”

That could explain why farmers and people who spend considerable time out in the sun may get fewer melanomas in chronically exposed skin, but the same number of the other type of melanoma as well as many other types of skin cancer that are related to chronic long term exposure.

Those “other types” of melanoma can occur anywhere, not just in areas exposed to the sun. The reason for the other type of melanoma is not fully known but genetics play a role. There are also drugs and diseases that decrease the immune system in the entire body, which increases the risks of all types of skin cancers including melanoma. Not knowing why is frustrating to doctor and patient, Stratman said.

“Most people don’t like randomness and want explanations for everything. But skin cells are constantly growing and being replaced and sometimes a cell makes a “mistake” and becomes cancerous, he noted. That can happen with any of the three skin cancer types mentioned earlier.

“I can’t give a specific cause as to why some cancers show up in mostly unexposed areas like the breasts, buttocks, eyelids, palms of the hands, under the toenails and behind the ears,” he said. Cancers also can spread to areas not exposed at all to the sun, such as the uterus, colon, lungs and prostate gland.

How you can spot skin cancer

As a dermatologist, he feels responsible for examining each of those areas but understands some people are uncomfortable with this.

To try to detect skin cancer yourself, especially melanoma, he recommends the “ugly duckling” rule.

“If you have a bunch of spots, I call it a family. You can have a little red dot family and a little brown dot family,” he said. “But if you see one that’s clearly bigger and has different colors, even someone without any training can pick out that ugly duckling. Most people can do that pretty well for melanomas and for other cancers that refuse to heal.”

You can also follow these 5 signs to spot a melanoma mole.

If you think you may have skin cancer, have it checked by your doctor, who may refer you to a dermatologist.

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