Hair cortisol and cortisone are decreased by natural sunlight.

Background And Aims: Hair glucocorticoids (cortisol and cortisone) are increasingly used as measures of long-term integrated exposure to glucocorticoid hormones. Glucocorticoids gradually disappear from the hair shaft, which may result from exposure to ultraviolet (UV) radiation in natural sunlight. We aimed to study the influence of sun exposure on hair glucocorticoids.

Material And Methods: Scalp hair samples were obtained from nine volunteers (median age 33 [range 21-81], 7 females), and part of each hair sample was exposed to three experimental conditions: repeated exposure to natural sunlight for 40h (natural UV), exposure to a high amount of artificial UV radiation, and storage in the dark (control). Hair cortisol (HairF) and cortisone (HairE) were quantified by liquid chromatography-tandem mass spectrometry.

Results: When compared to control, HairF was decreased in 9 out of 9 hair samples after natural sunlight exposure (median decrease -3.1pg/mg or -54%, P<0.001) and artificial UV radiation (-4.7pg/mg or -75%, P=0.003). HairE decreased in 8 out of 9 samples, both after natural sunlight (-7.6pg/mg or -32%, P=0.012) and artificial UV (-10.7pg/mg or -52%, P=0.026).

Conclusions: Exposure to natural sunlight decreases the glucocorticoid content of scalp hair, apparently through UV radiation, and is therefore an important confounder that should be considered in studies involving the measurement of hair glucocorticoids.