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Minoxidil, a vasodilator medication known for its ability to slow or stop hair loss and promote hair regrowth, was first introduced, exclusively as an oral drug, to treat high blood pressure. It was however discovered to have the important side-effect of increasing growth or darkening of fine body hairs; this led to the development of a topical formulation as a 2% concentration solution for the treatment of female androgenic alopecia or 5% for treating male androgenic alopecia. Measurable changes disappear within months after discontinuation of treatment. The mechanism by which it promotes hair growth is not fully understood. Minoxidil is a potassium channel opener, causing hyperpolarization of cell membranes and it is also a vasodilator, it is speculated that, by widening blood vessels and opening potassium channels, it allows more oxygen, blood and nutrients to the follicle. This can also cause follicles in the telogen phase to shed, usually soon to be replaced by new, thicker hairs in a new anagen phase. It needs to be applied regularly, once or twice daily, for hair gained to be maintained, and side effects are common. The most common adverse reactions of the topical formulation are limited to irritant and allergic contact dermatitis on the scalp. There have been cases of allergic reactions to the nonactive ingredient propylene glycol, which is found in some topical solution especially if they are galenic. Increased hair loss which can occur during Minoxidil use, is due to the synchronization of the hair cycle that the treatment induces. In this review, we described its mechanism of action, use in dermatology and some patents related to alternative treatment of allergic reactions due to its use.
Rossi et al. (Sun,) studied this question.