Androgenetic alopecia, or male pattern balding, is common. In fact, about 50 % of men will have androgenetic alopecia by age 50. It is well known that genetics and hormonal influences play an important role in men.
The role of ultraviolet radiation in male balding has been debated for many years and we still don't know all the answers. However, many scalp diseases are made worse by ultraviolet radiation. For example, individuals with seborrheic dermatitis will often report flares following sun exposure. In addition, patients with discoid lupus or dermatomyositis may note worsening after sun exposure.
The exact role of ultraviolet radiation in male balding is not clear. We know that inflammation is present under the scalp in many men with genetic hair loss and so the question arises... How did that inflammation get there? ... and is their any possibility that sun exposure contributes to the inflammation that is found under the scalp in men with balding?
An interesting study from researchers in Taiwan offers further clues that sunlight just 'might' contribute in some way to male balding. The researchers compared balding patterns in 758 policemen and 740 men in the general polulation. Interestingly, policemen aged 40 to 59 had a two-fold increased risk of having male balding. In addition, there was a statistically significant association between male balding and sunlight exposure.
More research is needed understand if and how ultraviolet radiation affects the process of male balding. If a link is found, it will be important to determine if men who reduce sun exposure (with hats, etc) will slow down the natural progression of the male balding process.
Su et al. Androgenetic alopecia in policemen: Higher prevalence and different risk factors compared to the general population. Arch Dermatol Res 3: 753-61.