Indoor tanning is linked to higher melanoma risk and widespread DNA damage in skin cells. Digest

Indoor tanning has long been linked to melanoma, the deadliest form of skin cancer, but the biological pathways connecting tanning bed exposure to melanoma are not fully defined.

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In a new study, researchers analyzed medical records from 32,315 dermatology patients, identifying 2,932 people with quantifiable indoor tanning exposure and comparing them with 2,925 age-matched patients who reported no tanning bed use. In a separate molecular analysis, they collected normal-appearing skin from the upper or lower back of 26 donors. This included patients from a skin cancer clinic who were tanning bed users with more than 50 self-reported lifetime sessions, controls from the same clinic who reported no tanning bed use, and deceased body donors whose tanning bed history was unavailable. They then analyzed the DNA of melanocytes, the pigment-producing cells that can give rise to melanoma.

• Melanoma was diagnosed in 5.1% of people with tanning bed exposure, compared with 2.1% of nonusers. After accounting for age, sex, sunburn history, and family history, tanning bed use was associated with almost three times higher odds of melanoma.
• Risk increased with the number of tanning bed sessions, forming a dose–response pattern that is often used to support causal inference in epidemiological studies.
• Among patients with melanoma, those who used tanning beds were more likely to have tumors on body areas that usually receive little everyday sun exposure and were more likely to develop multiple separate melanomas.
• Melanocytes taken from tanning bed users carried nearly twice as many mutations as those from control donors. This difference was most prominent on the lower back, which is usually covered outdoors but fully exposed during tanning sessions.
• Melanocytes from tanning bed users were more likely to contain pathogenic mutations, genetic changes known to help drive cancer, often affecting genes involved in the MAPK signaling pathway, a key growth-control system in melanoma.

Together, these findings suggest that tanning beds raise melanoma risk in two ways. They increase the total number of mutations inside melanocytes, and they spread this damage across a larger area of the body than natural sunlight typically reaches. This creates a wider pool of altered cells that are closer to becoming cancer.

The study relied on self-reported tanning histories and included a small number of skin donors, so larger studies will be needed to confirm and refine these patterns. Nevertheless, these new insights strengthen the biological case against claims that tanning beds are a safer alternative to sunlight. In this clip, I share 10 science-backed strategies to reduce cancer risk.