Have you ever slipped on some sandals, looked down at your toes, and noticed an unusual dark spot on your toenail? It’s possible you stubbed your big toe or dropped something heavy on your foot that caused bleeding underneath the nail. If so, expect that bruise to change in color from red, to purple, to dark brown or black as the blood is resorbed and a new nail grows out. But if you don’t recall any run-ins with the sofa and the mark doesn’t disappear after a few weeks, you might want to get your toenail checked for a certain—sometimes elusive—type of cancer.

What Is Toenail Melanoma?

You’ve likely heard of melanoma, a skin cancer that strikes the skin’s pigment-making cells, or melanocytes, but maybe not considered that means it could also crop up “under the hood” of your toenails and fingernails within the skin of your nail bed. Yikes.

There are actually numerous kinds of melanoma and this variant, called subungual (a.k.a. underneath-the-nail) melanoma, accounts for only 0.7% to 3.5% of malignant melanomas worldwide. “Subungual melanomas most often affect the big toe or thumbnail, which account for 75% to 90% of all cases,” says Dr. Rachel Westbay, M.D., a board-certified dermatologist at Marmur Medical in New York City.

Dr. Westbay also notes that there’s a higher prevalence of subungual melanomas in people of color, namely Black and Asian people: “It’s the most common types of melanomas diagnosed in deeply pigmented people, probably due to this population’s low incidence of cutaneous melanoma. In contrast to cutaneous melanoma, subungual melanoma does not appear to be related to sun exposure.” In perhaps the most noted example of how serious this form of melanoma can be, reggae icon Bob Marley tragically died when a subungual melanoma on his toe metastasized. The Jamaican singer believed that the dark spot under his toenail had instead been caused by a soccer injury.

When caught early and treated, though, the survival rate for subungual melanoma is high. At the earliest stage, the five-year survival rate is around 97%, and the 10-year survival rate is around 95%. The trick: Monitoring any spots on your nails, noting any changes, and seeing a dermatologist if their appearance seems suspicious.

Distinguishing Subungual Melanoma vs. Toenail Fungus

Your feet don’t get as much mirror time as other parts of your body but they can reveal certain signs of trouble with your health. Toenails (and fingernails), for instance, are one of the stealthy places where cancer can appear on your body.

So what exactly should you be on the lookout for? “In general, subungual melanomas present as a dark spot that is expanding, or a longitudinal pigmented streak that widens or extends to the skin around the nail,” says Erum Ilyas, M.D., a board-certified dermatologist based in King of Prussia, PA, with the Schweiger Dermatology Group. In other words, picture a vertical racing stripe that runs just beneath the nail down to your cuticle. Again, unlike a simple bruise (or subungual hematoma), this dark spot won’t fade away as the nail grows out.

According to Dr. Westbay, another telltale sign is the black or brown spot becoming wider and nonuniform in color. “If the pigment band becomes wider than 3 millimeters (mm), especially near the cuticle; becomes more irregular in pigmentation, such as a mixture of light and dark brown shades; or develops blurred borders extending to the skin around the nail fold [or, bottom of the nail], you have historical indicators of nail melanoma,” she says.

However, not all nail melanomas have a distinct shade. In fact, up to half of nail melanomas either have little pigment or completely lack pigment, says Dr. Westbay. That means any persistent pain, thinning, cracking, bleeding, or nail distortion should be monitored because a colorless nail melanoma could be the culprit.

Strangely enough, says Dr. Ilyas, a lot of patients coming in with concerns that they may have a nail melanoma have actually confused unsightly toenail markings with those that derive from a much more common condition, nail fungus. Both problems can cause discolored and misshapen toenails, but in the case of nail fungus, the toenails become yellowed and thickened—as opposed to thinner—and may crumble at the edges.

What Causes Subungual Melanomas vs. Toenail Fungus?

The exact cause of subungual melanomas is unknown. “Researchers do know, however, that this type of melanoma is different from others because it has no connection to sun exposure,” says Dr. Westbay. Risk factors for the disease include severe injury, damage, or trauma to the nail; having close family members with subungual melanoma; and genetic mutations with known predispositions to skin cancer.

Meanwhile, the cause of toenail fungus is clear-cut. According to the Cleveland Clinic, the infection usually occurs when certain fungi get through a “crack or cut in your toe,” allowing the invaders to embed between the toenail and the tissue just underneath. “Nail fungus, also known as onchyomycosis, develops as a result of a fungus under that nail plate, triggering a buildup of debris under the nail plate, thickening of the nail plate, and a white chalky residue,” explains Dr. Ilyas.

If your doctor is not able to diagnose toenail fungus on sight, they may take some nail clippings to be tested to determine the cause of your nail symptoms. Besides prescription oral and topical treatments, there are some over-the-counter creams like terbinafine (Lamisil) that can help—although treatment for toenail fungus isn’t always needed, per the Mayo Clinic. Talk to your health care provider to see which approach is right for you.

Subungual Melanoma Diagnosis and Treatment

If a dermatologist examines your toenails and finds any markings or physical signs to be concerning, they’ll most likely need a biopsy of the nail bed. “The nail itself is a bit of a window to see the skin underneath,” says Dr. Ilyas. “A biopsy of the skin under the nail plate is needed to see if the lesions fit the criteria suggestive of skin cancer.”

If a melanoma is detected via the biopsy, your dermatologist will determine what next steps are required to remove it. “If the melanoma is confined to the epidermis [top layer of skin], then it may be managed conservatively by wide surgical excision of the entire nail apparatus with margin control,” says Dr. Westbay. If the subungual melanoma has spread beyond the skin just below the nail and further into the toe itself, it is considered invasive. Although “traditionally, this has required complete amputation of the digit,” says Dr. Westbay, don’t panic: There is another approach that can preserve the bone and joints of the affected toe called Mohs micrographic surgery.

In this surgery, a thin layer of tissue at the cancer site is removed and studied under a microscope and examined for signs of cancer. The process is repeated until no signs of cancer are seen in the layer of tissue removed.

In cases of metastatic melanoma, where the cancer has spread beyond the toe to another area of the body, “immunotherapy agents are typically selected,” says Dr. Westbay.

When to See a Doctor

Many of us may take our feet for granted but it’s smart to give them some regular heel-to-toenail attention when we kick off our shoes, scrub them in the shower, or prep them for a pedicure. And if you notice unexplained discoloration in your toenails or symptoms like persistent pain, thinning, cracking, bleeding, or nail distortion, see your health care provider or dermatologist to have them examined. Remember: With early detection, subungual melanoma is highly curable, so stay calm and connect with a qualified dermatologist who can make a treatment plan specifically for you.

What Is Melanoma?

Melanoma is a type of skin cancer that’s diagnosed in almost 100,000 people per year, according to the American Cancer Society (ACS). Other forms of skin cancer, including basal and squamous cell carcinomas, are far more common. More than three million Americans develop these skin cancers each year.

Melanoma originates in the melanocytes, which are pigment-producing cells in your skin. Cancer develops when these cells grow out of control, creating a tumor in the skin, explains the ACS. What causes these cells to grow out of control? Usually, skin cancer cell growth is triggered by UV rays, which are in sunlight or tanning beds. However, genetics can also increase your risk for melanoma, says the ACS.

Melanoma is particularly dangerous because it can grow deep into skin tissues and metastasize, or spread, to other organs in the body.

Unfortunately, “melanoma is the deadliest form of skin cancer,” says Ravi K. Amaravadi, M.D., the scientific director of the Tara Miller Melanoma Center at the University of Pennsylvania in Philadelphia. According to the ACS, 8,000 people are expected to die of melanoma this year.

Melanoma can be diagnosed at stages 0, 1, 2, 3, and 4. “The vast majority of cases are picked up in earlier stages, as melanoma is visible on the skin, so people or their doctors may see a dark spot on the skin that’s changing,” says Dr. Amaravadi. Stage 0 means that the cancer is located only in the top layer of the skin. Stages 1 and 2 mean that the cancer is still within the skin but has grown thicker, while stage 3 indicates that it has spread to lymph nodes or nearby skin, according to the American Academy of Dermatology (AAD).

So what does a stage 4 melanoma diagnosis mean? This indicates that you have advanced melanoma that has spread elsewhere in your body. The most common places for melanoma to spread, according to the Melanoma Research Alliance, are:

• Brain

• Gastrointestinal tract

• Liver

• Lungs

Stage 4 can also be diagnosed when the cancer has spread to distant skin or lymph nodes, says the AAD.

What Does Stage 4 Melanoma Look Like?

A changing mole is often how melanoma first appears on the skin, according to the National Cancer Institute. The acronym ABCDE is often used to describe how melanoma looks:

“It’s important to know the spots on your body, and if something is new or changing, bring it to the attention of your doctor or dermatologist,” says Marc Hurlbert, Ph.D., chief executive officer of the Melanoma Research Alliance in Washington, DC.

Stage 4 Melanoma Diagnosis

To be diagnosed with melanoma, the AAD says that your doctor will take your personal and family medical history, perform a head-to-toe skin check, and may also examine a specific spot of skin.

If there is a spot on your skin that looks suspicious, your dermatologist can take a biopsy where it will be examined by a pathologist for cancer cells. For melanoma that may have metastasized (or spread), imaging tests, such as an x-ray, ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), or positron emission tomography (PET) scans may also be used, notes the ACS, to locate where tumors have spread.

How Is Stage 4 Melanoma Treated?

Treatment for stage 4 metastatic melanoma typically involves a combination of approaches aimed at controlling the cancer, managing symptoms, and improving your quality of life. Certain factors will determine your treatment plan, says Hurlburt, including:

• Genetic mutations in your tumor

• If you qualify for a clinical trial

• Likelihood of recurrence

• Where your melanoma has spread

• Your overall health

The choice of treatment and the prognosis for stage 4 melanoma can vary widely among individuals. Some patients may achieve long-term remission or stable disease with the available therapies, while others may face more challenging circumstances. It’s essential for patients with stage 4 melanoma to work closely with a multidisciplinary health care team, including oncologists, surgeons, and palliative care specialists, to determine the most appropriate treatment plan based on their unique situation and goals of care. Here are the treatments your doctor may talk to you about:

Immunotherapy

Immunotherapy drugs (a.k.a. “immune checkpoint inhibitors”) like Keytruda (pembrolizumab) and Opdivo (nivolumab) assist your own immune system in a cancer cell search and destroy mission.

Your immune system recognizes cancer cells as your own cells, not foreign invaders, so it allows them to grow unabated. Immune checkpoint inhibitors, however, wake up your immune system. “These drugs take the brake pedals off the immune system, allowing it to find and kill the melanoma tumor, similar to how your immune system would kill a bacterial or viral infection,” says Hurlburt.

Immunotherapy is often used before surgery, a protocol called neoadjuvant therapy. Clinical trials show that this protocol is superior at preventing recurrence of cancer compared to giving the drugs after surgery, explains Dr. Amaravadi.

Radiation

Radiation therapy is a common cancer treatment that uses high doses of radiation to damage the DNA of cancer cells, which slows down their growth, kills them, and can shrink tumors, according to the National Cancer Institute. By shrinking tumors, this treatment is often used to relieve melanoma symptoms or manage pain.

Radiosurgery

A specialized technique called gamma knife radiosurgery may be used for people whose melanoma has spread to their brain. “This can affect your thinking, neurological function, and produce seizures,” says Dr. Amaravadi. “It’s the worst-case scenario for melanoma, and we still don’t have great treatments for these patients.” He calls this treatment, “the next frontier” because it’s a specific type of radiation where gamma rays are targeted directly at a specific tumor, thus saving the surrounding healthy tissue.

Surgery

In some cases, surgery may be performed to remove isolated metastatic lesions that may be causing painful symptoms. It’s also used to remove some tissue surrounding the cancer and any affected lymph nodes.

Targeted Therapy

These are drugs that can be used in patients who have specific genetic mutations and fall under the “precision medicine” umbrella of cancer care. Doctors can test the genetics of your tumor. If it has a specific mutation, called a BRAF mutation, then you can use a BRAF inhibitor medication, like Zelboraf (vemurafenib). “These are very effective at shrinking tumors rapidly,” says Dr. Amaravadi.

Outlook for Stage 4 Melanoma

Despite the seriousness of a metastatic melanoma diagnosis, there is a lot of reason to remain optimistic. “It used to be the case that the prognosis was dismal—almost a 0% five-year survival rate,” says Dr. Amaravadi. “But now we can say that there’s likely a 50% chance of five-year survival, even with stage 4 disease. That’s pretty amazing.”

Why? It’s all because of the shift and expansion in treatment options, as well as successful clinical trials that have paved the way for these new drug treatments.

“New drugs have changed the entire paradigm of how we treat melanoma. We encourage patients to discuss the possibility of a clinical trial sooner rather than later,” adds Hurlburt. “In today’s trials, you’re randomized to a new drug being studied or put into a control group where you get one of the amazing 15 drugs that have already been approved.” (You can use the melanoma clinical trials search function on the Melanoma Research Alliance’s website, curemelanoma.org to find one you may qualify for.)

Clinical trials are especially important for certain patients. “If patients have really aggressive stage 4 melanoma, many of the [approved] treatments don’t work. These are the patients who we’re trying to find new treatments for,” says Dr. Amaravadi. If your tumor does not respond to current FDA-approved treatments, a clinical trial may be right for you. It’s through these types of clinical trials that all of the currently used drugs that are now helping patients live longer lives were approved, says Dr. Amaravadi.

How to Get Support

If you’ve been diagnosed with metastatic melanoma, it’s wise to seek out a medical oncology group that sees a high volume of melanoma patients, says Dr. Amaravadi.

It’s also important to connect with friends, family, and other people going through a melanoma diagnosis, too. CancerCare, for example, offers a free, 15-week online support group for people diagnosed with melanoma who are currently receiving treatment. Don’t go through this diagnosis alone. Identify those individuals that you can lean on through the highs and lows of your cancer journey.

The Bottom Line

Stage 4 melanoma is metastatic melanoma, a type of skin cancer that has spread to another part of the body. Melanoma is the deadliest form of skin cancer and it is responsible for the deaths of about 8,000 Americans per year. However, recent advancements in treatment have greatly increased the survival rate, and there are many options to treat this type of cancer. “It seems as if we are gaining a foothold on melanoma. New ideas are continuing to be generated on how to treat the most resistant forms of the disease,” says Dr. Amaravadi.

You hear about ultraviolet rays all the time, usually in the context of skin cancer, a disease that affects an estimated one in five Americans. But what do ultraviolet rays actually do? “The sun emits three major forms of energy: visible light that you see; thermal energy, or the heat that you feel; and ultraviolet, or UV, radiation that technically has no light or heat associated with it,” explains Erum Ilyas, M.D., a board-certified dermatologist based in King of Prussia, PA, with the Schweiger Dermatology Group. “There’s a spectrum of UV rays with varying energy levels that come through the atmosphere from the sun.”

The three forms of UV rays (or radiation) are UVA, UVB, and UVC, each representing a different range of wavelengths of energy. “The shorter wavelengths have higher energy and can penetrate the skin to damage the DNA of our cells,” says Dr. Ilyas. A wavelength, or the distance between two peaks of a light wave, is measured in nanometers (nm): UVA rays are longest, in the 315 nm to 400 nm range; UVB are shorter in length, in the 280 nm to 315 nm range; and UVC are the shortest, in the 100 nm to 280 nm range.

“Although UVC rays have the shortest wavelengths of UV energy, the atmosphere effectively blocks it from reaching the earth,” says Dr. Ilyas—that’s why you don’t hear any warnings about them. It’s the other two that you need to be mindful of.

The Impact of UVA Rays on Your Health

According to Dr. Ilyas, UVA radiation isn’t typically linked to any specific type of skin cancer, including melanoma. “But it certainly contributes to long-term damage to skin that can make it more susceptible to damage by UVB rays—including melanoma formation—as we age,” she says. “When you hear UVA, think of the ‘A’ standing for aging of the skin.”

UVA rays penetrate into the skin’s dermis (a.k.a. middle layer) where collagen and elastin fibers are found. Damaging those fibers lowers our skin’s elasticity, and without elasticity, skin can’t snap back into place after making facial expressions or movements—leading to lines, wrinkles, and sagging. “Think of the thin skin under our eyes, if you pinch it then release, the skin has a little lag time before it settles back into place. That’s a loss of elasticity,” says Dr. Ilyas. “You can blame UVA exposure for this.”

The Impact of UVB Rays on Your Health

Just as the “A” in UVA can stand for aging, think of the “B” in UVB as standing for burn. “UVB rays are the type of UV radiation that is associated with sunburns and skin cancer,” says Dr. Ilyas. “When we purchase SPF-containing sunscreen products, the SPF factor is related to the amount of UVB blocked from the product and does not tell us the amount of UVA blocked.”

Because UVB rays have higher energy than UVA rays, they have an ability to wreak more havoc on our DNA. “UVB is directly linked to DNA damage,” she says. Our cells naturally have the ability to repair the DNA through mechanisms within our cells, but if the stress on our cells is significant or prolonged, the repair mechanisms can become impaired. Once the damage is done, if DNA does not have the opportunity to repair itself, then skin cancer, such as melanoma, has the potential to develop, notes Dr. Ilyas.

Needless to say, you want to have a strong sun protection game (more on that later). “The most SPF that skin itself can offer, irrespective of skin tone, is about SPF 13,” says Hysem Eldik, M.D., a board-certified dermatologist at Marmur Medical in New York City. That won’t cut it for keeping skin cells safe.

The Benefits of UVA and UVB Rays

All this news about the sun’s damaging effects getting you down? Not to worry, there is also a unique health perk that comes from spending time in the sun. When your skin is exposed to sunlight, it naturally makes vitamin D from the cholesterol in your skin cells. (Relax, this kind of cholesterol is good for you.) “Vitamin D is crucial for bone health, especially during childhood,” says Dr. Ilyas. “More and more studies are linking low vitamin D levels to colon cancer, heart disease, and breast cancer.”

So how much sun is enough to get an adequate dose of vitamin D, or the 600 to 800 international units (IU) recommended daily for adults? Well, that depends on a number of factors, including your skin tone, clothing coverage, location, the season, and the time of day you head outside. One study crunched the numbers for sunlight conditions at noon in Boston, MA, and Miami, FL, in each season and computed the impact on all different skin types. The upshot? Just a few minutes of sun at high noon was enough to do the trick in some cases.

As noted in the study, vitamin D synthesis occurs faster in individuals with lighter skin, and more slowly in those with darker skin tones. The main takeaway: It doesn’t take long to get a good dose of D from the sun, so don’t overdo the basking in the name of getting your vitamins.

When Are UV Rays the Strongest?

The midday hours, noon especially, are “peak UV exposure” time, but there can be other factors that can influence the actual UV around us. “Clouds, altitude, time of year, distance from the equator can all impact the amount of UV we are exposed to or the amount we think we are exposed to,” says Dr. Ilyas. “The highest incidences of skin cancer are actually found during ski season at higher altitudes.” In other words, don’t let the lack of heat give you a false impression that the risk of excess UV exposure is lower. “Remember thermal energy is different from UV radiation. UV does not have temperature associated,” she says.

The best advice for figuring out when your UV exposure is at its lowest is to check a weather app. If you scroll down, you’ll likely find a UV index for your time and the location. Another trick: Check out your shadow! “If your shadow is shorter than you, then the sun is directly above your head with the highest risk of UV exposure,” Dr. Ilyas says. “If your shadow is taller then it’s likely less intense.”

How to Protect Yourself from UVA and UVB Rays

Even though the sun’s ultraviolet rays are powerful, the tools for blocking its harmful effects are readily available. There are skincare products with sun protection factors (SPF) and clothing with an ultraviolet protection factors (UPF).

As for the type of sunscreen, both Dr. Ilyas and Dr. Eldik agree that you need to look for an SPF of at least 30 or higher (a UPF of 30 is also ideal). Dr. Eldik also cautions folks with darker skin not to believe the misconception that their skin can’t be damaged by UV radiation. “The natural SPF protection from a darker complexion simply isn’t enough to protect a person from UVA or UVB rays,” he says. “Those with dark skin need the same protection needed for lighter skin types, meaning guidelines for SPF still apply.”

Whether you’re deciding between a chemical sunblock (which neutralizes UV rays) or a physical block (which deflects them)—your sunscreen questions answered here—heed the following best practices, per our experts:

• Look for a sunscreen labeled broad-spectrum, meaning it protects against both UVA and UVB rays, with an SPF of at least 30.

• Reapply after two hours in the sun, or after swimming or sweating.

• Apply sunscreen everywhere. Get someone to help apply it in hard-to-reach areas like your back.

• Wear it every day. Sitting in front of a window or driving to work during the daytime still counts as sun exposure, and cloudy days still have UV rays.

• Check those expiration dates—sunscreen has a shelf-life of about three years and if the product has been exposed to heat, that shelf-life gets shorter.

And remember that clothing can play an important role in keeping your skin safe, too—after all, people do make sunscreen mistakes. “Although seeking broad-spectrum coverage implies UVA coverage, it does not tell you how much,” says Dr. Ilyas. “A better way to block both UVA and UVB is through sun-protective clothing. The UPF factor that clothing is gauged by gives an indication of both UVA and UVB protection.”

Bottom line: Enjoying a sunny day can be good for your overall well-being, and by protecting your skin from harmful ultraviolet rays, you can slash your risk of getting skin cancer—including melanoma—while also slowing down the effects of aging on your skin.