The cumulative exposure to indoor tanning and squamous cell carcinoma (SCC) risk is the same regardless of duration of use and age at initiation, according to a study published in JAMA Dermatology.
The cohort study included data from women born between 1927 and 1963 who were included in the Norwegian Women and Cancer study, which was established in 1991 with follow-up data available through December 31, 2015.
Participants received baseline questionnaires between 1991 and 2007, and follow-up questionnaires were given every five to seven years.
A total of 159,419 women (mean age at inclusion, 49.9 years) were included in the study. During a mean follow-up of 16.5 years, 597 women were diagnosed with SCC. Risk of SCC increased with increasing cumulative number of indoor tanning sessions.
Risk of skin cancer
The adjusted hazard ratio (HR) for highest use versus never use was 1.83 (95% CI, 1.38-2.42; P<0.001). Compared with never users, the following women had a significantly higher risk of SCC: those with 10 years or less of use (HR=1.41; 95% CI, 1.08-1.85), more than 10 years of use (HR=1.43; 95% CI, 1.16-1.76), age 30 years or older at initiation (HR=1.36; 95% CI, 1.11-1.67), and age younger than 30 years at initiation (HR=1.51; 95% CI, 1.18-1.92).
The researchers observed no significant association between age at initiation and age at diagnosis (estimated regression coefficient = −0.09; 95% CI, −1.11-0.94] for age at initiation of 30 years or older and −0.02; 95% CI, −1.27 to 1.22; for less than 30 years versus never use).
“The findings provide supporting evidence that there is a dose-response association between indoor tanning and SCC risk among women,” the researchers concluded.