Most adults have between 10 and 40 moles—which are small clusters of pigment-producing skin cells. Some people, especially those with lighter skin, may have many more. Those moles may change in size and appearance over the years, and in rare instances, a mole may become a melanoma, the most potentially deadly skin cancer.

But if you’re like most people, you don’t examine your moles or have a doctor check them periodically to see whether changes may signal a possible skin cancer. In fact, a survey of 476 people published in The Journal of Clinical and Aesthetic Dermatology found that only 25 percent reported checking their skin monthly and 17 percent reported that they did it just once a year.

That may be due, in part, to confusion over how effective regular skin checks are at finding possible skin cancers. So should you or a physician check your skin? If so, how often? Here’s what you need to know about changing moles and skin cancer risk.

Can All Moles Cause Skin Cancer?

Common moles are those we’re born with or develop until about age 40. They can change or even disappear over the years, and very rarely become skin cancers. Some, but not all, research suggests that having lot of those common moles (more than 50) may increase the risk of melanoma.

More worrisome are so-called atypical moles. They often appear during puberty but can pop up throughout life. They’re not skin cancers but can have some features of melanoma, such as irregular borders.

And while the vast majority of these never turn into melanomas,  they are more likely than common moles to become cancerous. Having five or more atypical moles is linked to a higher than normal risk of “thick,” or more advanced, melanoma. (Many melanomas start as pigmented moles, but the two more common skin cancers, basal cell and squamous cell carcinoma, don’t. They arise on their own from normal skin.)

Why do some moles change from benign to cancerous? Genetics seems to play a roled. And though melanoma can occur in areas that are usually shielded from sunlight, ultraviolet radiation seems to be a significant factor. For example, moles exposed to UV radiation, such as from from the sun or tanning beds, can mutate, triggering the abnormally rapid cell division that characterizes cancer, according to a 2015 study in the New England Journal of Medicine by Boris C. Bastian, M.D., professor of dermatology and pathology at the University of California, San Francisco, and colleagues.

Most melanomas, however, don't develop from exisiting moles. And reates of the cancer, which increase with advancing age, have been rising  for at least 30 years. Unnoticed, melanoma can grow and spread quickly, so experts agree that finding it early is key. “A melanoma the size of a dime has a 50 percent chance of having spread,” says Darrell S. Rigel, M.D., a skin cancer expert at the NYU School of Medicine.

Pros and Cons of Checking for Skin Cancer

While having a doctor check your skin for skin cancers seems like it would make sense, in 2009 the U.S. Preventive Services Task Force, an independent expert panel that advises the government on screening tests, concluded that there was insufficient evidence to recommend for or against regular skin checks by physicians. And in July 2016, the Task Force reaffirmed that conclusion, saying that there still is not clear evidence that regular professional skin exams saves lives by identifying cancers early.

But that doesn't mean that you should avoid those exams, says Jessica Krant, M.D., clinical assistant professor of dermatology at SUNY Downstate Medical Center in Brooklyn, N.Y., and a member of Consumer Reports’ medical advisory board.

For one thing, the Task Force didn't look at people at high risk of skin cancers. And it only looked at exams from primary care health care providers, not dermatologists. Moreover, catching melanomas early is key: unnoticed, the cancers can grow and spread quickly. “A melanoma the size of a dime has a 50 percent chance of having spread,” says Darrell S. Rigel, M.D., a skin cancer expert at the NYU School of Medicine.

For those reasons, many experts and organizations, such as the American Academy of Dermatology, recommend that you regularly do skin self-checks and have screenings by a physician to monitor moles.

Exactly how often you should do that is unclear, and depends in part on your chance of developing the disease. People at high risk should probably see a physician at least once a year, preferably a dermatologist, says Krant.

Key skin cancer risk factors include a history of sunburns, fair skin, light eyes, red or blonde hair, a family history of melanoma, or a personal history of basal cell or squamous cell cancer. (Screenings can also help pinpoint the latter two skin cancers, which are more common but not as deadly as melanoma.) People at very high risk, or with a history of melanoma, should be screened even more often.

Self checks are also important. Krant recommends a monthly or every other month schedule. (A study in the journal Archives of Dermatology found that 44 percent of melanomas were discovered by patients.) Use the commonly accepted ABCDE method.

And if you spot new moles or are unsure whether a mole's changes may be meaningful, see a dermatologist. Sometimes, a melanoma may not resemble other melanomas in shape, color, or size, says Scott W. Fosko, M.D., chair of dermatology at the Mayo Clinic in Jacksonville, Fla. For example, he says, the unusual amelanotic melanoma has little to no color.