Melanoma develops when the DNA inside pigment-producing skin cells called melanocytes becomes damaged, triggering uncontrolled growth. About 2.2 percent of people will be diagnosed with melanoma at some point in their lifetime, and an estimated 112,000 new cases are expected in the United States in 2026 alone. The causes range from ultraviolet radiation and genetic mutations to immune system changes, and not all melanomas trace back to sun exposure.
How UV Radiation Damages Skin Cell DNA
The most well-understood cause of melanoma is ultraviolet radiation, which harms your skin cells in two distinct ways depending on the type of UV light involved.
UVB radiation (the kind responsible for sunburns) is absorbed directly by DNA inside melanocytes. It forces neighboring molecules in your DNA strand to bond together abnormally, creating defects called pyrimidine dimers. These dimers distort the DNA structure and, when cells copy their genetic code to divide, the distortion leads to misreadings. The signature error is a specific type of mutation frequently found in the p53 gene, a critical gene that normally acts as a brake on cell growth. When p53 is knocked out by these mutations, damaged cells can keep dividing instead of being flagged for destruction.
UVA radiation (the longer-wavelength light that penetrates deeper into skin and passes through windows) works differently. Rather than damaging DNA directly, UVA generates reactive oxygen species, essentially unstable molecules that attack DNA from the inside. Melanin, the pigment that gives skin its color, actually amplifies this process. That’s a cruel irony: the very molecule meant to protect your skin can sensitize cells to oxidative damage under UVA exposure. Research from the Proceedings of the National Academy of Sciences found that melanocytes accumulate significantly more oxidative DNA damage from UVA than other skin cell types, making them uniquely vulnerable.
To make things worse, melanocytes are also less efficient at repairing DNA damage compared to other skin cells. This combination of higher damage and slower repair is a key reason melanoma originates specifically in these cells rather than in the surrounding skin.
Sunburns, Tanning Beds, and Cumulative Exposure
Not all UV exposure carries equal risk. Intense, intermittent sun exposure, the kind that causes blistering sunburns, is more strongly linked to melanoma than steady, moderate exposure. Five or more sunburns over your lifetime more than doubles your melanoma risk.
Indoor tanning is particularly dangerous. Using tanning beds before age 20 increases your chances of developing melanoma by 47 percent, and the risk climbs with each session. Women younger than 30 who tan indoors are six times more likely to develop melanoma than those who don’t. Overall, indoor tanning can more than double melanoma risk. Tanning beds emit concentrated doses of both UVA and UVB, delivering the same DNA damage mechanisms described above in a compressed timeframe.
Gene Mutations That Drive Melanoma Growth
Once DNA damage accumulates, specific gene mutations determine whether a melanocyte becomes cancerous. These mutations hijack the cell’s growth signaling pathways, essentially flipping the “grow and divide” switch permanently on.
The most common is a BRAF mutation, found in 40 to 50 percent of cutaneous (skin-surface) melanomas. BRAF normally helps regulate cell growth, but when mutated, it sends constant signals telling cells to multiply. About 15 to 20 percent of melanomas carry NRAS mutations instead, which activate a related growth pathway. These two mutations are almost never found together in the same tumor.
A smaller subset of melanomas, particularly those arising on the palms, soles, or mucous membranes, follow a different genetic pattern. BRAF and NRAS mutations are rare in these tumors, but 15 to 40 percent carry KIT mutations. This distinction matters because the location and genetic profile of a melanoma influence how it’s treated.
Skin Type and Genetic Predisposition
Your baseline skin characteristics significantly affect your risk. People with the lightest skin tones (those who burn easily and rarely tan) face the highest melanoma risk. In studies of eye-related melanoma, 85 percent of patients had the lightest skin classifications. People with the lightest skin were also more likely to develop higher-grade tumors with more aggressive genetic profiles, and they had the greatest 10-year risk of metastasis (25 percent compared to 14 to 15 percent for those with medium skin tones).
Beyond skin color, inherited traits play a role. Having a large number of moles, a family history of melanoma, or naturally red or blond hair all increase susceptibility. Some families carry inherited mutations in genes that regulate cell growth or DNA repair, giving melanocytes fewer defenses against the accumulation of damage over time.
Melanoma Without Sun Exposure
Not all melanomas are caused by UV radiation. Acral lentiginous melanoma, which develops on the palms, soles of the feet, or under fingernails, occurs on skin that rarely sees sunlight. The exact cause remains unknown, though researchers have explored potential links to physical trauma and stress on these areas. This subtype is the most common form of melanoma in people with darker skin tones, and its distinct biology underscores that UV avoidance alone doesn’t eliminate melanoma risk entirely.
How a Weakened Immune System Contributes
Your immune system continuously surveys the body for abnormal cells, including early-stage cancer cells. When that surveillance is suppressed, melanoma risk rises. Solid organ transplant recipients, who take long-term medications to prevent organ rejection, face up to an 8-fold higher melanoma risk compared to the general population. These immunosuppressive drugs reduce the body’s ability to detect and destroy mutated melanocytes before they form tumors. Some of these medications may also directly promote cell proliferation through pathways independent of the immune system.
People with conditions that weaken the immune system, such as HIV or certain autoimmune diseases requiring immunosuppressive treatment, face a similar elevation in risk.
Do Moles Turn Into Melanoma?
A common assumption is that melanoma typically develops from an existing mole that “turns cancerous.” In reality, roughly 85 percent of melanomas appear as entirely new spots on the skin rather than growing out of a pre-existing mole. Atypical moles (moles that are irregularly shaped, multicolored, or larger than a pencil eraser) do carry some increased risk, but the vast majority of them never become melanoma.
This is why monitoring your skin for new spots is just as important as watching existing moles for changes. A spot that appears suddenly and grows, changes color, or looks different from your other moles warrants attention regardless of whether it developed from a mole that was already there.
How These Causes Work Together
Melanoma rarely results from a single event. It typically develops through an accumulation of factors: repeated UV damage over years, a genetic background that makes DNA repair less efficient, specific mutations that activate growth pathways, and an immune system that fails to catch the abnormal cells early enough. A person with fair skin who had severe childhood sunburns and uses tanning beds is stacking multiple risk factors, each compounding the others. Understanding which factors apply to you helps clarify where your personal risk falls and which exposures matter most to minimize.