This study used data from studies on both mice and humans.

For the mouse experiments, the investigators exposed the skin of shaved mice to either a low dose (50 millijoules per square centimeter; mJ/cm²) or an active dose (800 mJ/cm²) of ultraviolet B (UVB) light per day for 8 weeks. The active dose was comparable to 20 to 30 minutes of midday sun exposure and did not produce a sunburn.

The human studies employed several different designs and cohorts.

First, the investigators recruited 19 people (ages 23 to 73) with skin conditions who were undergoing phototherapy; they received a dose of 0.1 to 2.5 J/cm² twice or three times per week. Before the treatment and then 1 month after, investigators administered an adapted Passionate Love Scale (PLS) questionnaire, which assesses passion, attraction, and sexuality-related feelings about romantic partners. The investigators also administered a questionnaire evaluating aggression.

Next, the investigators recruited 19 people (ages 18 to 55) to avoid the sun for 2 days and then expose themselves to 25 minutes of midday sun (estimated ultraviolet light dose of 2,000 mJ/cm²). The investigators assessed levels of sex hormone markers both the day before and shortly after sun exposure.

Finally, the investigators used data on 13,086 men (ages 21 to 25) from a cohort study in Israel to assess average testosterone levels by month of the year. They also examined differences in testosterone levels by month among men from countries with low (<2,500 joules per square meter; J/m²) or high (≥4,500 J/m²) amounts of ultraviolet radiation (UVR), a proxy for skin color (which can influence the absorption of ultraviolet light).

Ultraviolet light exposure influences hormones and sexual behavior Original paper