The claim that indoor tanning increases the risk of melanoma by 75% was first presented in a 2006 report from the International Agency for Carcinogenic Research (IARC), which reported a 75% increase in melanoma incidence among sunbed users whose first sunbed use occurred before age 35.
On its face, this result is in the noise zone of epidemiology. According to the National Cancer Institute*:
In epidemiologic research, [risks of less than 100 percent] are considered small and usually difficult to interpret. Such increases may be due to chance, statistical bias or effects of confounding factors that are sometimes not evident.
One of the major problems in tanning studies is that researchers don’t know how much ultraviolet radiation (outdoor or indoor) any study subjects actually received.
Past this Achilles heel, a reanalysis of the IARC claim by University of Delaware epidemiologist Mia Papas reported that when limited to professional salons, the statistical association between indoor tanning and melanoma essentially vanished, becoming a statistically insignificant increase of six percent — i.e., a zero association, practically speaking.
Reference:
* National Cancer Institute. “Abortion and possible risk for breast cancer: analysis and inconsistencies [press release]”. Washington (DC): 1994 Oct 26.