How Does Skin Cancer Develop in Areas of Skin That Aren't Exposed to Sun?

If sun exposure causes skin cancers, how is it that some skin cancers grow in body parts that never see the light of day?

If there's any downside to the success of skin cancer awareness campaigns, it's the common misperception that the sun is the only cause of skin cancer. It's not.

While sun exposure is the most common cause of skin cancer to develop in areas of unprotected skin, it may develop in other areas. This is especially the case with melanoma, the deadliest form of skin cancer. Melanoma may form in hidden areas, such as under fingernails or toenails and on the bottom of the feet. It is also possible to develop melanoma in your eye. Though it is less common, other types of skin cancer can also develop in areas that are not usually exposed to the sun.

THE CANCER TRIGGER

Like all cancers, skin cancers are the result of changed or damaged genes that lead to cells being able to grow and invade other tissues.

Left untreated, cancer cells overrun the body, and can be deadly.

With most cancers, there is a cumulative set of circumstances: a series of “hits” to the body. Sun exposure could be responsible for more than one of those hits over time; in some people, repeated UV exposure might be enough to trigger skin cancer.

GENETICS, HORMONES AND CHEMICAL EXPOSURE

Genetics also play a factor. It is the strongest ‘non-sun’ factor.

About 10 per cent of melanomas occur in people with a family history of melanoma. In these people, the odds a skin cancer will be in a hidden body part are higher than for others.

But melanomas can occur in hidden parts of the body even where there isn't any obvious family history.

Exposure to certain chemicals, and even pregnancy hormones are also contributing factors to skin cancer.

Related: Melanoma Symptoms and Detection

DON’T IGNORE A SPOT

While such skin cancers are rare, if you notice something new or unusual on your skin, don’t ignore it.

Skin cancer in a hidden part of the body is actually more likely to be a melanoma, the most dangerous type of skin cancer. When caught early, there is a 98%. But it is fast-spreading and early treatment is critical.

Non-melanoma skin cancers, basal cell and squamous cells, can sometimes occur in non-sun-exposed areas too. Non-melanoma cancers are less deadly because they are slower to spread, but they still require prompt treatment. If left untreated, they can be just as deadly.

"You need to get to know what your skin looks like and if you think a spot or mole is changing: getting darker, changing in pigmentation, size, shape, itching, or bleeding – then get it checked by a dermatologist immediately.", says skin cancer specialist and Little Leaves Clothing co-founder Dr. Carlos Gomez-Meade.