If You Notice This On Your Fingernails, Get Checked for Cancer, Experts Warn

It's often mistaken for another common ailment. Here's when to call the doctor.

Skin cancer can take many shapes and forms. While some cancers are localized and easily treated at a dermatologist's office, others can easily spread and become life-threatening. Knowing what to look for is crucial in early detection, which can make all the difference in your prognosis. Caught early, localized melanoma has a five-year survival rate of over 98 percent—but if it spreads to distant parts of the body, that number drops dramatically, to just 30 percent. Read on to learn how to spot one particular sign of melanoma that could be hiding in plain sight on your fingernails.

READ THIS NEXT: If You Feel This in Your Throat, Get Checked for Cancer.

"Hidden melanomas" are a rare but potentially dangerous type of skin cancer.

Dermatologist inspecting patient for skin cancer

Melanoma is widely considered the deadliest form of skin cancer, given its ability to spread to the lymph nodes and distant parts of the body. Most often, melanoma appears as a growth on the skin in areas with high levels of sun exposure, but there are exceptions to this rule.

"Melanomas can also develop in areas of your body that have little or no exposure to the sun, such as the spaces between your toes and on your palms, soles, scalp or genitals," explains the Mayo Clinic. "These are sometimes referred to as hidden melanomas because they occur in places most people wouldn't think to check."

READ THIS NEXT: If You Notice This on Your Hands, Get Checked for Cancer.

If you see this on your fingernails, get checked for cancer.

Woman using emery board on fingernails

One place that hidden melanoma can develop is under a fingernail or toenail. When this happens, it's known as acral-lentiginous melanoma (ALM) or sometimes simply as acral melanoma. This type of melanoma can also be found on the hands, palms, and soles of the feet.

Subungal melanoma, one of the most common subtypes of acral melanoma, presents as a brown or black streak or blotch of pigmentation on the nail. "The discoloration can progress to thickening, splitting, or destruction of the nail with pain and inflammation," says a 2021 study published in Stat Pearls. Most often—in 75 to 90 percent of cases—these changes appear on the big toe or the thumbnail.

It's the most common kind of melanoma among certain ethnic groups.

Unrecognizable woman looking at her nails, while removing her nail polish.
GoodLifeStudio / iStock

Acral melanoma is considered rare among the general population, accounting for only up to 3.5 percent of all malignant melanoma cases, according to the 2021 study. However, it's still the most common form of melanoma among certain ethnic groups, since other types of melanoma are less common in those populations.

"Melanoma of the nail apparatus occurs equally in all racial groups. However, it is the most common variant of malignant melanoma of African-Americans, Asians, and Hispanics. It accounts for 75 percent of melanomas in African populations, 25 percent in Chinese populations, and 10 percent in Japanese populations," the study explains. "These groups usually have a very low incidence of cutaneous malignant melanoma due to the melanin pigment protecting their skin from ultraviolet (UV) radiation from the sun," the researchers add.

For more health news sent directly to your inbox, sign up for our daily newsletter.

This kind of pigmentation can have other causes.

Podiatrist treating feet during procedure
Inside Creative House / iStock

One thing that can make acral melanoma difficult to identify is how similar it can sometimes look to injuries of the nail bed, known as hematomas. Like acral melanoma, hematomas are often brown or black in color, and can present as a streak or blotch under the nail.

The key difference is that typically, when a hematoma is to blame, you'll recall the injury that caused it. However, running, hiking, and playing sports can cause hematomas on the toenails absent major trauma to the nail bed. According to Medical News Today, a fingernail hematoma may take between two to three months to heal, while a toenail may take up to nine months to heal. If you notice that the change in pigmentation lasts longer than that, or if you do not recall a trauma that could have caused the discoloration, consult your doctor or dermatologist.

Lauren Gray
Lauren Gray is a New York-based writer, editor, and consultant. Read more
Filed Under