10 things you don’t know about melanoma

You may have heard of melanoma, but chances are also good that you don’t know everything you need to stay safe—it’s a tricky disease. Many people associate melanoma with moles that go bad, especially in fair-skinned people who don’t use sunscreen, but it’s not quite that simple.

To learn more about who’s at risk for melanoma and the surprising ways it can manifest, we spoke with Dr. Angela J. Lamb, assistant professor of Dermatology of the Icahn School of Medicine at Mount Sinai. Read on for 10 things you probably didn’t know about melanoma.

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It’s one of the most common cancers in young adults
Melanoma may be the least common skin cancer, but according to the American Academy of Dermatology (AAD), it’s the most common form of cancer for young adults ages 25 to 29 and the second most common cancer for people aged 15 to 29. Experts believe this is a result of tanning bed use, Lamb said.

It affects people of all skin tones
It’s true that people with more pigment in their skin have a much lower risk of skin cancer because they have more protection from the sun, but that doesn’t give them a free pass to skip sunscreen. Basal cell and squamous cell carcinomas—the most common types of skin cancer and those most strongly linked to sun exposure—rarely happen in people of color, and melanoma is also rare, but when it does happen, it’s mostly on palms and soles,  she said.

“I don’t tweak my recommendations based on what the patient looks like,” she said. “I tell everybody ‘wear sunscreen every day like it’s your job, make it a daily regimen like brushing your teeth.’”

Lamb also tries to drive home sunscreen’s anti-aging benefits for people who may not be sold on the cancer-prevention angle alone. In case you missed it: A 2013 study published in the Annals of Internal Medicine proved that daily sunscreen use helps prevent premature aging caused by sun exposure, including wrinkles and dark spots. Score!

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It may not develop in an existing mole
“This idea that bad moles turn into melanoma, some pathologists believe that and some don’t,” she said. “There are some who believe that you can have a bunch of moles and those will be fine, but you can get a melanoma in some other place.”

It can happen in people with few or no moles
Yes, melanoma symptoms include a change in the shape, size, or color of a mole and the more moles you have, the greater your risk for melanoma. But even people who don’t have a lot of moles are at risk for melanoma, Lamb said.

It may not be a mole at all
Melanomas can also look like a bruise that doesn’t heal or a dark streak under a fingernail or toenail, she said. Bob Marley was diagnosed with melanoma under one of his toenails in July 1977. He reportedly ignored advice to amputate the toe and the cancer spread to his lungs and brain, and he died in May 1981 at age 36. Melanoma can also appear in your eyes, but it’s exceptionally rare.

“If people are having blurry vision in one eye or pressure behind one eye, they should probably get screened for ocular melanoma,” Lamb said. The symptoms usually aren’t in both eyes, and regular screenings aren’t necessary because it is so rare.

It can appear in areas not exposed to the sun
Like between your fingers and toes, and on your underarms, butt, and genitals.

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It’s booming in older adults, too
Melanoma is also on the rise in Baby Boomers, who didn’t have access to modern sunscreens in childhood.

“Those folks were growing up during the time where people would literally lay out with reflectors and baby oil,” Lamb said. For people in their 50s and 60s who had a lot of sun exposure when they were younger, a melanoma diagnosis is the manifestation of genetic mutations to their melanocytes, cells that produce the skin pigment melanin, she says.

It’s the deadliest form of skin cancer…
While basal and squamous cell carcinomas are more common than melanoma, they have higher survival rates. According to the AAD, one American dies from melanoma every hour. In 2014, it’s estimated that more than 9,700 deaths in the United States will be attributed to melanoma.

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…but it’s highly treatable when caught early
“The earlier you catch a melanoma, the better the survival,” Lamb said. “It’s directly correlated.”

The five-year survival rate for people whose melanoma is detected and treated before it spreads to the lymph nodes (stage III melanoma) is 98 percent, according to the AAD. Lamb said we may be seeing higher numbers of melanoma cases because doctors are better able to diagnose Stage 0 melanoma, or melanoma in situ, where there are visible changes on the skin’s surface but cancer hasn’t yet developed in the epidermis. The Skin Cancer Foundation recommends yearly skin cancer exams, which can help catch melanoma as early as possible.

It doesn’t only strike sun-worshippers or tanning bed users
People with a family history of melanoma can be more prone to it than the rest of the population. Reports have shown that having a first-degree relative with melanoma—that is, a parent, brother, or sister—can increase your lifetime risk by 10-15 percent, Lamb said. That’s why it’s so important to know your specific skin cancer history.

“Skin cancer tends to get lumped together,” she said. “You need to know if your grandmother at 80 had a basal removed or if your brother at 50 had a melanoma removed—that’s a big difference.”

This article originally appeared on Health.com.