The pathogenesis of hair loss, the postulated mechanisms of minoxidil action on 
hair growth, and clinical trials, adverse reactions, experimental formulations, 
and percutaneous absorption of topical minoxidil preparations are reviewed. 
Topical minoxidil seems to normalize hair follicles and increase blood flow to 
the scalp. In clinical trials of various formulations, results have varied. 
Improved hair growth occurred after four to six months of therapy; twice-daily 
application seems to be indicated. The most frequently reported adverse 
reactions are mild scalp dryness and irritation and, rarely, allergic contact 
dermatitis. Current recommendations are to reserve topical minoxidil for 
patients with normal cardiovascular status and to routinely monitor blood 
pressure, heart rate, and electrocardiographic changes. A new drug application 
is pending with FDA for use of topical minoxidil in androgenetic alopecia 
(male-pattern baldness), which is genetically determined and apparently 
stimulated by androgens. For alopecia areata, which involves hair loss on the 
body or scalp, usually patchy and of sudden onset, no reliable treatment has 
been found, although minoxidil may be efficacious in some patients. Minoxidil 
has generated new interest in hair-loss research. The etiology of hair loss must 
be better understood before more effective treatment regimens can be designed.