Seasonal variation of salivary testosterone in men, normally cycling women, and women using hormonal contraceptives

► Little is known about humans' testosterone variation over long timescales (i.e., seasons). ► Men and normally-cycling (NC) women have significant seasonal testosterone variation. ► Men's and NC women's testosterone is maximal in the fall/winter and minimal in the spring/summer. ► Women using hormonal contraceptives have a flatter seasonal testosterone profile than NC women.