Table 3.

First exposure at early age to indoor tanning, annual frequency of indoor tanning use, and the risk of melanoma and non-melanoma skin cancer (NMSC).

Exposure	Study N	Summary RR (95% CI)	Heterogeneity
			I2 (%)	p-Value
Cutaneous melanoma
First exposure at early age to indoor tanning (year) 1
<20	9	1.47 (1.16–1.85)	61	<0.01
≥20	9	1.28 (1.01–1.63)	77	<0.01
Annual frequency of indoor tanning (times) 2
<10	6	1.33 (1.00–1.78)	60	0.03
≥10	6	1.52 (1.22–1.89)	0	0.67
Non-melanoma skin cancer
First exposure at early age to indoor tanning (year) 3
<20	6	2.02 (1.44–2.83)	68	<0.01
≥20	6	1.48 (1.31–1.68)	0	0.56
Annual frequency of indoor tanning (times) 4
<10	3	1.32 (1.14–1.52)	40	0.19
≥10	3	1.56 (1.31–1.86)	41	0.18
Squamous cell carcinoma
First exposure at early age to indoor tanning (year)
<20	3	1.89 (0.90–3.98)	75	0.02
≥20	3	1.53 (1.26–1.85)	27	0.25
Annual frequency of indoor tanning (times)
<10	2	1.46 (1.24–1.71)	0	0.97
≥10	2	1.65 (1.30–2.10)	10	0.29
Basal cell carcinoma
First exposure at early age to indoor tanning (year)
<20	2	1.86 (1.44–2.41)	0	0.61
≥20	2	1.51 (1.19–1.92)	0	0.69
Annual frequency of indoor tanning (times)
<10	2	1.29 (1.01–1.65)	40	0.20
≥10	2	1.46 (1.28–1.66)	18	0.27

¹ For Swerdlow et al. in 1988, an estimate of age at first indoor tanning device use <30 years and ≥30 years; for Westerdahl et al. in 2000, an estimate of age at first indoor tanning device use ≤35 years and >35 years; for Lazovich et al. in 2010, an estimate of age at first indoor tanning device use <18 years and ≥18 years; for Chen et al. in 1998, Cust et al. in 2011, and Elliott et al. in 2012, an estimate of age at first indoor tanning device use <25 years and ≥25 years; for Farley et al. in 2015, an estimate of age at first indoor tanning device use ≤19 years and >19 years were used. ² For Zhang et al. in 2012, an estimate of the number of tanning device use <6 times/year and 6+ times/year; for Stenehjem et al. in 2017, an estimate of the number of indoor tanning device use 1–2 times/month and 3–5 times/month; for Ghiasvand et al. in 2019, an estimate of the number of indoor tanning device use <15 times/lifetime and 15+ times/lifetime were used. ³ For Ferrucci et al. in 2012, an estimate age at first indoor tanning device use ≤18 years and >18 years; and for Simon Lergenmuller et al. in 2019 an estimate age at first indoor tanning device use <30 years and ≥18 years were used. ⁴ For Ferrucci et al. in 2012, an estimate of 1–18 indoor tanning sessions and >18 sessions; and for Zhang et al. in 2012, an estimate of ≤6 times/year and >6 times/year were used.