Melanoma develops when the pigment-producing cells in your skin, called melanocytes, accumulate DNA damage that causes them to grow uncontrollably. Ultraviolet radiation is the primary driver, but genetics, skin type, mole patterns, and certain inherited mutations all play a role. With an estimated 112,000 new cases expected in the U.S. in 2026, melanoma is one of the most common cancers, yet its causes are well understood enough to meaningfully reduce your risk.
How UV Radiation Damages Skin Cells
Sunlight contains ultraviolet radiation that can physically alter the DNA inside melanocytes. When UV rays hit these cells, they create abnormal bonds between DNA building blocks, essentially corrupting the genetic instructions the cell uses to grow and divide. UV also triggers the production of unstable molecules called reactive oxygen species, which cause additional oxidative damage to DNA.
Over time, this damage can disable genes that normally keep cell growth in check while simultaneously switching on genes that promote it. When enough of these mutations accumulate in a single melanocyte, the cell loses its built-in growth controls and becomes cancerous. This process can take years or even decades, which is why a severe sunburn in childhood can contribute to a melanoma diagnosis decades later.
UVB vs. UVA: They’re Not Equal
Not all ultraviolet light contributes to melanoma in the same way. UVB radiation (the shorter wavelength responsible for sunburns) is the primary initiator. Research published in Cancer Research found that in animal models, only UVB-containing light sources triggered melanoma. Mice exposed to UVA alone, even at doses 33 times higher than the effective UVB dose, developed melanoma at the same rate as unirradiated animals.
This distinction matters practically. UVB is strongest between 10 a.m. and 4 p.m. and is partially blocked by glass. UVA penetrates deeper into the skin and passes through windows, but based on current evidence, it does not appear to initiate melanoma on its own. Both wavelengths cause skin aging and other forms of damage, but UVB carries the more direct cancer risk because of how it corrupts DNA in melanocytes.
Sunburn Patterns Matter More Than Total Exposure
One of the more counterintuitive findings in melanoma research is that intense, intermittent sun exposure is more dangerous than steady, chronic exposure for certain types of melanoma. Superficial spreading melanoma and nodular melanoma, the most common variants, typically develop on skin that only gets occasional intense sun, like the torso of someone who works indoors but vacations at the beach. A history of sunburns, particularly during childhood, roughly doubles the risk for these types.
Chronic, cumulative sun exposure leads to a different variant called lentigo maligna melanoma, which tends to appear on the faces and forearms of older adults and outdoor workers. Interestingly, sunburns themselves don’t seem to be a significant risk factor for this type. The two patterns of exposure create different molecular damage in melanocytes, though researchers still don’t fully understand why.
Tanning Beds Carry Serious Risk
Indoor tanning beds emit concentrated UV radiation, and the risk they pose is substantial. A systematic review by the International Agency for Research on Cancer found that any tanning bed use before age 35 is associated with a 75 percent increase in melanoma risk. That’s not a minor bump. Because tanning beds deliver high doses of UV in short sessions, they replicate the intermittent, intense exposure pattern most strongly linked to melanoma.
Genetic Mutations That Drive Melanoma Growth
When melanoma develops, the cancer cells almost always carry specific genetic mutations that fuel their growth. The most common is a mutation in a gene called BRAF, found in about 43 percent of primary melanomas. Another 15 percent carry mutations in a gene called NRAS. Together, these two mutations account for roughly 58 percent of all primary melanomas. In tumors that have already spread, the frequency rises to 63 percent.
These mutations aren’t ones you’re born with. They’re acquired over your lifetime, largely through UV damage. They cause cells to receive a constant “grow” signal that never shuts off. Identifying which mutation a melanoma carries has become critical for treatment, because targeted therapies can block the specific growth signals these mutations create.
Inherited Risk: Family History and Gene Variants
Some people inherit gene variants that make their melanocytes more vulnerable to becoming cancerous. The most well-studied is a variant in the CDKN2A gene, which normally produces a protein that prevents cells from dividing too quickly. In families with multiple melanoma cases who carry this variant, the estimated lifetime risk of developing melanoma by age 80 is 67 percent. In the broader population, carriers of CDKN2A variants have a lifetime risk between 19 and 35 percent, depending on the specific mutation.
Having a first-degree relative with melanoma increases your risk even without a known gene variant. This likely reflects a combination of shared genetics (skin type, mole patterns, DNA repair efficiency) and shared environmental exposures.
Skin Type and Mole Patterns
Your natural skin characteristics are among the strongest predictors of melanoma risk. People with very fair skin that always burns and never tans (Fitzpatrick skin types 1 and 2) face the highest risk. Those with medium skin that sometimes burns carry moderate risk. People with deeply pigmented skin that rarely or never burns have substantially more natural UV protection, but melanoma can still occur.
Moles are another important marker. Having more than five atypical moles (larger, irregularly shaped moles with uneven color) increases melanoma risk roughly tenfold compared to someone with none. These moles aren’t necessarily pre-cancerous themselves, but their presence signals that your melanocytes are more prone to abnormal growth. Other physical traits that raise risk include red or blonde hair, blue or green eyes, and a tendency to freckle heavily.
Melanoma in Places the Sun Never Reaches
Not all melanomas are caused by UV exposure. Acral lentiginous melanoma develops on the palms, soles of the feet, and under fingernails or toenails, areas that get little to no sun. This type has not been conclusively linked to UV radiation and is the most common form of melanoma in people with darker skin.
Researchers believe genetic predisposition plays a significant role in acral lentiginous melanoma, but the exact triggers remain unclear. Melanoma can also develop in the eyes (uveal melanoma) and in mucous membranes lining the mouth, nasal passages, or digestive tract. These non-skin melanomas reinforce that while UV radiation is the dominant cause overall, melanocytes can become cancerous through pathways that don’t involve sun exposure at all.
Weakened Immune System
Your immune system plays a constant surveillance role, identifying and destroying abnormal cells before they can form tumors. People with suppressed immune systems, whether from organ transplant medications, certain autoimmune conditions, or HIV, face a higher risk of melanoma because their bodies are less effective at catching and eliminating these early cancerous cells. This is also why melanoma risk increases with age: immune function naturally declines over time, giving damaged cells a better chance of surviving and multiplying.