Background : Ultraviolet light radiations (UVR) may be responsible for hair cycle synchronization and telogen effluvium in the animal and humans. The effect if any of cumulative UVR on chronic hair shedding and androgenic alopecia (AGA) is largely unknown. Objective : To compare the severity of AGA with the extent in solar elastosis. Method : The present study combining immunohistochemistry and computerized image analysis was undertaken in 140 men with AGA and 50 non-alopecic men. Solar elastosis was identified using the antibody to lyzozyme, and collagen was revealed by sirius red staining. The number and diameter of hair shafts were also assessed. Results : The scalp dermis was significantly thicker in AGA than in unaffected subjects. The difference was mainly due to a more severe elastosis in baldness. The earliest signs of solar elastosis preceded hair thinning. When elastosis was thicker than 0.2 mm, a negative exponential correlation was found between hair diameter and severity in solar elastosis. Conclusion : Chronic UVR exposure of the scalp may affect the hair cycle and be one exogenous factors influencing negatively the progression of AGA. The induction of stress-induced premature senescence (SIPS) through reactive oxygen species and microinflammation might be operative at the level of the follicular stem cells.