The link between sun exposure and skin cancer is well established, but uncommon signs of skin cancer aren’t always as obvious. Just because an area rarely sees sunlight doesn’t mean you’re in the clear. Skin cancer can develop in unexpected places—from the nail beds to the soles of your feet and even the eyes. While most cases do appear on commonly exposed areas like the face, neck and ears, knowing where else to look can help you catch something serious early.
And the warning signs aren’t always obvious. Beyond changes in moles or new growths, lesser-known red flags—such as vision changes, dark streaks under the nails or lesions in intimate areas—can also signal skin cancer.
Ahead, dermatologists break down the subtle warning signs, where they can show up and how to check your skin from head to toe.
Not All Skin Cancer Is Caused by the Sun
About 10 percent of skin cancers aren’t directly caused by UV exposure, according to New York dermatologist and spokesperson for The Skin Cancer Foundation, Ariel Ostad, MD. These can appear anywhere—from the palms and nail beds to the scalp and genitals.
So what’s behind them? Wainscott, NY dermatologist and founder of MACRENE Actives, Macrene Alexiades, MD, explains that viruses can play a role. “While peri- and subungual squamous cell carcinoma (SCC) is the most common type of skin cancer on the nail, it appears first as a wart-like growth that grows quickly and can form a hard surface,” Dr. Alexiades explains. “As a matter of fact, wart virus has been shown to cause SCC around the fingernail.”
Uncommon Signs of Skin Cancer and Where They Appear
Skin Cancer on the Palms and Soles
Skin of color is often more resistant to UV light thanks to higher levels of melanin, but that can lead to a dangerous misconception. “When a person of color gets skin cancer, it’s often found on the soles of the feet and the mucous membranes, which are rarely or never exposed to the sun,” Dr. Ostad explains. “Acral lentiginous melanoma (ALM), a very severe form of the disease, is more common among darker-skinned people.”
Because these areas aren’t typically checked, cancers here are more likely to go unnoticed. “These melanomas tend to appear on parts of the body not often exposed to the sun and often remain undetected until after the cancer has spread,” Dr. Ostad says. ALM commonly presents as a dark brown or black discoloration on the soles, palms or under the nails.
Skin Cancer Under the Nails
Melanoma can also develop beneath the nails. Famously, Bob Marley’s was first identified under his toenail after an injury that didn’t heal.
“Cancer under the nails can be either a melanoma or a squamous cell carcinoma (SCC),” Dr. Ostad explains. “Sun exposure is a major factor in melanoma on the nails, but trauma and injury can also lead to melanoma on the nails. HPV is also a major cause of cancer under the nails, along with possible trauma as a cause.”
Dr. Alexiades notes that dark streaks are one of the most important warning signs. “Melanoma under the nail can look like bruises, brown or black streaks or lines, so it’s important to keep a close eye on any dark areas by the cuticles,” she says.
To reduce risk, sun protection still matters—even here. “Limit your sun exposure and apply sunscreen to the skin around your nail bed and don’t wash it off,” Dr. Alexiades says. “Make sure to reapply SPF directly after. Look for a broad-spectrum sunscreen. Many nail polishes also have built-in protection to help preserve color from UV exposure. For those at higher risk, gloves are recommended, especially during outdoor activities.”
Skin Cancer in the Eyes
UV exposure doesn’t just affect the skin—the eyes are vulnerable, too. Ocular melanoma is aggressive and can spread to other parts of the body, most commonly the liver. Early signs may include changes in pupil size or shape, bulging eyes or shifting position in the socket. Dark spots on the iris are another key warning sign. These cancers may also cause vision changes, including blurriness or partial vision loss.
Both Dr. Ostad and Dr. Alexiades recommend wearing UV-protective sunglasses daily. “I recommend wearing sunglasses anytime you’re out in the sun, no matter the season, as damage to the eyes can happen year-round,” Dr. Alexiades says.
Skin Cancer in Intimate Areas
“Skin cancers, primarily squamous cell carcinoma (SCC), in the genitals are generally due to human papilloma virus (HPV),” Dr. Ostad explains.
“Melanomas can also arise in the genitals from pre-existing moles. It is important to have those areas examined during your annual visit by a dermatologist.”
These cancers may take years—even decades—to develop after initial HPV exposure. That’s why regular, thorough skin checks are so important, even in areas you might not think to examine.
What to Look For
The ABCDE rule is a helpful guideline for evaluating moles: asymmetry, irregular borders, multiple colors, diameter larger than six millimeters and evolving changes in size, shape or symptoms such as itching or bleeding.
“It’s also important to watch for the ‘ugly duckling’ sign,” Dr. Collins says. “That’s a mole that looks noticeably different from the rest.”
Dr. Beer notes that some warning signs are more obvious. “Sores that don’t heal—especially in sun-exposed areas—can be a sign of squamous cell carcinoma or basal cell carcinoma,” he says. “Lesions that are rapidly growing or painful should be evaluated more urgently.”
How to Check Yourself at Home
A monthly self-check is one of the most effective ways to catch skin cancer early. “Start in a well-lit room with both a full-length mirror and a hand mirror,” says Austin, TX dermatologist Kristina Collins, MD. “Examine your face, scalp, ears, neck, chest and abdomen first, then move to your arms, hands, nails, legs, feet and the soles of your feet. Don’t forget hidden areas like the back, buttocks and between the toes.”
Taking a methodical, head-to-toe approach helps ensure nothing is missed. “In general, patients should try to take a systematic approach, starting with the face to monitor for any new, persistent or worsening lesions,” says Washington, D.C. dermatologist Jacob Beer, MD. “Pictures can be helpful to monitor lesions as well as to share them with their dermatologist at their next skin check.”
When Skin Cancer Has No Visible Symptoms
Perhaps most concerning, not all skin cancers present in obvious ways.
“Some skin cancers can develop in areas that are hard to see or may initially appear very subtle,” Dr. Collins explains. “Not all skin cancers are dark or raised. Some can look like a small pink patch, a persistent pimple or even a scar-like area.”
“Amelanotic melanomas can present as skin-colored lesions that rapidly progress,” Dr. Beer adds. “There are also rare neuroendocrine tumors on the skin that can have very subtle findings or look like benign processes such as cysts and can grow quickly and potentially metastasize.”
How to Prevent Skin Cancer
While not all skin cancers are caused by the sun, most still are—and prevention remains critical. Washington, D.C. dermatologist Tina Alster, MD, explains that even early sun exposure can have long-term consequences. “A single blistering sunburn in one’s teens increases the risk of melanoma several fold,” she says.
Plymouth, MA dermatologist and spokesperson for The Skin Cancer Foundation, Ramzi Saad, MD, emphasizes a layered approach. “No single sun protection method can protect you perfectly,” he explains. “Clothing is the first line of defense against the sun, providing consistent protection that doesn’t wear off over time. Don’t forget a hat and UV-blocking sunglasses.”
When to See a Doctor for Skin Cancer
If you spot anything unusual—whether it’s a changing mole, a non-healing sore or a new lesion—it’s time to get it checked. “In general, I recommend about yearly for most of my patients,” Dr. Beer says. “For patients who have a personal or family history of skin cancer, I’ll typically recommend more frequent visits every 4-6 months.”
Early detection can make all the difference. When caught early, treatment is typically simpler—and far more effective.
