Melanoma develops when the pigment-producing cells in your skin, called melanocytes, accumulate DNA damage that causes them to grow uncontrollably. Ultraviolet radiation from sunlight or tanning beds is the most common trigger, but genetics, skin type, mole patterns, and even physical trauma can play a role. An estimated 112,000 new cases will be diagnosed in the United States in 2026 alone.
How UV Radiation Damages Skin Cells
The most direct path to melanoma starts with ultraviolet light. When UV rays hit your skin, they physically distort the DNA inside melanocytes, creating lesions called cyclobutane pyrimidine dimers. These are spots where two neighboring DNA letters fuse together, and when cells try to copy that damaged stretch during division, they introduce permanent errors into the genetic code. Over years, those errors can accumulate in genes that control cell growth, flipping them into an always-on state.
UVB radiation (the wavelengths responsible for sunburn) is the primary driver. It produces the specific mutation patterns most commonly found in melanoma tumors. UVA radiation, the longer-wavelength light that penetrates deeper into skin and dominates tanning beds, also damages DNA but appears to be surprisingly limited in its ability to cause mutations in melanocytes directly. That doesn’t make UVA safe. It contributes to skin aging, suppresses immune defenses in the skin, and works alongside UVB to increase overall cancer risk.
Sunburns, Tanning Beds, and Cumulative Exposure
Not all sun exposure carries the same weight. Intense, intermittent burns appear to be more dangerous than steady, moderate exposure. Blistering sunburns in childhood and adolescence are particularly harmful because younger skin cells divide more rapidly, giving damaged DNA more opportunities to replicate errors before repair mechanisms can fix them.
Indoor tanning is one of the clearest avoidable risk factors. Using a tanning bed before age 35 increases melanoma risk by 59 percent, according to a meta-analysis cited by the American Cancer Society Cancer Action Network. Tanning beds concentrate UV output at intensities that can exceed midday sun, and sessions tend to expose large areas of skin that rarely see natural sunlight.
Skin Type and Natural Protection
Your baseline level of melanin, the pigment that gives skin its color, acts as a natural UV shield. People with fair skin, light eyes, and red or blond hair produce less of the protective form of melanin, leaving their DNA more exposed to radiation damage. Epidemiological data consistently shows that melanoma incidence is inversely correlated with the amount of melanin in your skin, meaning darker-skinned populations develop it far less often.
Geography reinforces this pattern, but only for lighter-skinned groups. Among non-Hispanic white populations in the U.S., residential UV exposure explains a large share of the variation in melanoma rates from one region to another. For Black, Hispanic, Asian/Pacific Islander, and Native American populations, the link between local UV levels and melanoma incidence is not statistically significant, suggesting that higher melanin levels effectively neutralize much of the geographic UV difference.
That said, darker skin is not immune. Melanoma in people with more pigmented skin is often diagnosed later, at a more advanced stage, partly because both patients and doctors may not be looking for it. The types that occur in darker skin also tend to arise in places unrelated to sun exposure, like the palms, soles, and nail beds.
Moles and Atypical Nevi
The number and type of moles on your body is one of the strongest visible predictors of melanoma risk. Having many common moles raises your baseline risk, but the more critical marker is the presence of dysplastic nevi, which are moles that look irregular: uneven borders, multiple colors, or a diameter larger than a pencil eraser. Someone with more than five dysplastic nevi has roughly 10 times the melanoma risk of someone with none.
Most dysplastic nevi never become melanoma themselves. They serve more as a signal that your melanocytes are prone to abnormal growth. If you have several, a dermatologist will typically recommend annual full-body skin exams to catch any changes early.
Genetic and Family Risk
About 5 to 10 percent of melanomas run in families. The best-studied inherited mutation involves a gene called CDKN2A, which normally acts as a brake on cell division. When that brake is broken, melanocytes can proliferate unchecked. In a population-based study, carriers of a CDKN2A mutation had roughly a 14 percent chance of developing melanoma by age 50 and a 28 percent chance by age 80.
Beyond single-gene mutations, melanoma tumors themselves carry characteristic genetic changes. Approximately 38.5 percent of melanoma patients have mutations in the BRAF gene, 16.4 percent in NRAS, and 10 percent in KIT. These aren’t mutations you’re born with. They develop in the tumor itself over time and are now used to guide treatment decisions. The most common of these, a specific BRAF change called V600E, accounts for 60 to 80 percent of all BRAF mutations in melanoma and is the target of several effective therapies.
Melanoma Without Sun Exposure
Some melanomas appear in places the sun never reaches: the soles of the feet, under fingernails or toenails, inside the mouth, or on internal mucosal surfaces. Acral lentiginous melanoma, the type that develops on palms and soles, is the most common form of melanoma in people with darker skin, and it has no clear connection to UV exposure.
Researchers have found that chronic mechanical stress may play a role. In a study of 95 patients with acral melanoma, 61 percent of tumors appeared on stress-bearing areas of the foot (the parts that absorb the most pressure during walking), and nearly 19 percent of patients reported a history of direct trauma at the tumor site. This doesn’t mean an injury causes cancer, but repeated physical stress to an area may promote conditions that allow abnormal cells to take hold.
Mucosal melanomas, which arise in the lining of the nose, throat, or genital tract, remain poorly understood. They lack the UV-associated mutation signatures of skin melanomas and are thought to involve different, still-unidentified triggers.
How Multiple Risk Factors Add Up
Melanoma rarely results from a single cause. It typically emerges from the intersection of several risk factors acting over years or decades. A person with fair skin, a history of childhood sunburns, more than five atypical moles, and a first-degree relative with melanoma faces a meaningfully different risk profile than someone with just one of those factors. Immune suppression, whether from organ transplant medications or other conditions, further raises the odds because the immune system normally detects and destroys abnormal cells before they gain a foothold.
The practical takeaway: UV exposure is the one major risk factor you can control. Genetics, skin type, and mole patterns are fixed, but limiting unprotected sun exposure and avoiding tanning beds removes the most common source of the DNA damage that starts the process.