Ultraviolet (UV) radiation is the primary type of light that causes skin cancer. Specifically, UVB and UVA rays from sunlight are responsible for the DNA damage that drives the vast majority of skin cancers, with UVB being the more potent mutagen of the two. An estimated 104,960 new cases of invasive melanoma and over 107,000 cases of early-stage melanoma are projected in the United States in 2025 alone, and the true number of skin cancers is far higher because the most common types aren’t even tracked by most cancer registries.
UVB: The Most Direct Cause
UVB radiation spans wavelengths of about 290 to 315 nanometers. These rays don’t penetrate very deep into your skin, reaching only about 10 to 20 micrometers below the surface (roughly the thickness of the outermost layer). But what UVB lacks in depth, it makes up for in destructive precision. UVB photons are absorbed directly by DNA in your skin cells, physically fusing together neighboring building blocks on the DNA strand. These fused segments, called pyrimidine dimers, are the signature lesion of UV-induced skin cancer.
When your cells try to copy DNA that contains these fused segments, the copying machinery often misreads the damaged code. The most common error is a specific letter swap (C to T) at the damage site. If enough of these mutations pile up in genes that control cell growth, a cell can begin dividing uncontrollably. This is how the squamous cell and basal cell carcinomas that account for the bulk of skin cancers get started. UVB is considered the more powerful mutagen because these DNA lesions persist for a long time in skin cells, giving the damage more opportunity to become permanent.
UVA: Deeper Penetration, Indirect Damage
UVA radiation (315 to 400 nanometers) penetrates significantly deeper than UVB. Measurements of human skin show UVA reaching 60 to 135 micrometers below the surface depending on body location, which means it passes through the outer skin layer and into the living tissue beneath. UVA makes up roughly 95% of the UV radiation that reaches Earth’s surface, so your cumulative exposure to it is enormous.
Rather than directly warping DNA the way UVB does, UVA primarily works through an indirect route. It generates reactive oxygen species, unstable molecules that ricochet through your cells and damage DNA, proteins, and cell membranes. These reactive molecules can also interfere with p53, a protein your body relies on to detect damaged cells and either repair them or trigger their self-destruction. When that safety net fails, damaged cells survive and keep dividing. UVA plays a particularly important role in melanoma, the most dangerous form of skin cancer, because it reaches the deeper-sitting pigment-producing cells that UVB cannot easily access.
UVC and Germicidal Lamps
UVC radiation (100 to 280 nanometers) is the highest-energy form of ultraviolet light and is extremely harmful to living cells. Sunlight contains UVC, but Earth’s ozone layer absorbs virtually all of it before it reaches the ground. The main source of UVC exposure for most people is artificial: germicidal lamps used to disinfect air, water, and surfaces. Conventional germicidal lamps emit at 254 nanometers and are a recognized human health hazard, capable of causing skin cancer and cataracts with direct exposure. That’s why these lamps are typically used in unoccupied spaces or shielded fixtures.
A newer technology uses “far-UVC” light at 222 nanometers. At this shorter wavelength, the light is so strongly absorbed by proteins in the outermost dead skin cells that it cannot reach the living cells underneath. Studies using 3D human skin models show that 222-nanometer light kills bacteria effectively while producing almost no detectable DNA damage in skin tissue. This is why far-UVC is being explored for use in occupied rooms, though it remains a newer technology under ongoing evaluation.
Tanning Beds Concentrate the Risk
Indoor tanning beds emit about 12 times more UVA radiation than the midday sun. Because UVA penetrates deep into the skin and generates oxidative damage to DNA, this concentrated exposure carries serious cancer risk. People who use tanning beds before age 35 have a substantially elevated risk of melanoma. The intensity is the key problem: a tanning session delivers a massive dose of UVA in a compressed time frame, overwhelming your skin’s ability to repair the damage as it accumulates.
Blue Light and Screens
High-energy visible light, commonly called blue light, sits just beyond UVA on the spectrum at roughly 380 to 480 nanometers. It’s emitted by the sun, LED screens, and indoor lighting. Lab studies on isolated skin cells show that blue light at high doses can generate reactive oxygen species and cause DNA damage, including chromosomal abnormalities in keratinocytes. However, the doses used in these experiments are far higher than what you’d receive from a phone or computer screen. At the low intensities typical of everyday device use, current evidence does not show that blue light significantly induces oxidative stress in skin. This is an area where the gap between laboratory conditions and real-world exposure is large.
Infrared and Heat Exposure
Infrared radiation, the type of light you feel as warmth, has a more uncertain relationship with skin cancer. Years of heavy infrared exposure can cause a condition called erythema ab igne, a mottled skin discoloration from chronic heat. Case reports over decades describe skin cancers occasionally developing in areas affected by this condition, typically after 15 to 20 years of repeated exposure. Epidemiological data suggest infrared radiation may contribute to premature skin aging and possibly carcinogenesis, but there is no clear, direct evidence linking infrared exposure to skin cancer the way there is for UV radiation. For most people, infrared is not a meaningful skin cancer risk.
Compact Fluorescent Bulbs
Some compact fluorescent lamps (CFLs) emit small amounts of UV radiation, particularly unshielded bulbs with defects in their phosphor coating. Measurements show that the worst-performing CFLs can produce measurable UVB emissions at mercury spectral lines (294, 297, 302, and 313 nanometers). Even with eight hours of daily exposure to the highest-emitting bulbs tested, it would take one to three weeks to accumulate a dose equivalent to a single minimal sunburn unit. For most people, this level is clinically insignificant. For individuals with diagnosed photosensitivity conditions, however, the cumulative UV from unshielded CFLs is not negligible, and enclosed or shielded bulb designs dramatically reduce the emission.
What Matters Most for Protection
The overwhelming driver of skin cancer is ultraviolet radiation from the sun, with UVB causing the most direct DNA mutations and UVA contributing through deeper penetration and oxidative damage. Tanning beds amplify the risk by delivering concentrated UVA at intensities far beyond natural sunlight. Other light sources, including screens, household bulbs, and infrared, contribute little to no meaningful risk for the general population.
Broad-spectrum sunscreen blocks both UVA and UVB, which is why the “broad-spectrum” label matters more than SPF number alone. SPF measures protection against UVB only. Clothing, shade, and timing your outdoor activity to avoid peak UV hours (roughly 10 a.m. to 4 p.m.) reduce exposure from both wavelengths simultaneously. Your skin type plays a role in how quickly damage accumulates: lighter skin absorbs more UV per unit of time, but all skin tones can develop UV-induced DNA damage and skin cancer.