SHEDDING DUE TO CHEMICAL AGENTS
* Minoxidil
For the same reasons that minoxidil promotes hair growth, it can also cause shedding. Despite many years of research and use, the exact physiologic mechanisms whereby minoxidil stimulates hair growth is not known. The stimulatory effect of minoxidil on the hair follicle can cause hair that is in the telogen phase to shed before the end of the normal 100-day telogen period.
The effect of minoxidil on the hair follicles is dose dependent. The initial shedding was rarely reported during use of topical 2% minoxidil. With 5% topical minoxidil, it was usually not noticeable, but was infrequently reported. With the use of currently available minoxidil concentrations of 12.5%, the initial shedding is commonly reported. The shedding can be noted within weeks of initial use of topical minoxidil.
Since shedding due to the use of topical minoxidil only effects hair that is in the telogen phase, the increased shedding should not last longer than 100 days and should only effect those areas of the scalp where the topical minoxidil is being applied.
* Finasteride (Propecia / Proscar)
There have been multiple reports of excessive shedding several months after finasteride therapy. Typically, there is a good response to finasteride to prevent or reverse male pattern baldness. Then, around the 11th to 16th week, there can be sudden shedding, sometimes on a massive scale. The entire phenomenon fits the description of a telogen effluvium. It is a common observation that post-partum women often suffer the same temporary hair loss. In the case of finasteride use, the telogen effluvium appears to be a reaction to the sudden change in the systemic levels of the sex hormone, DHT. Often the cause of a telogen effluvium are obscure, but has been related to high fevers, stress, trauma, medications, etc.
The shedding is generally diffuse (global) and can affect areas of the scalp not usually affected by male pattern baldness. So, it would be common to note shedding from the sides and back of the head in addition to the crown, vertex and frontal areas. The shedding tends to be fairly symmetrical, but will be more noticeable in the areas affected by male pattern baldness, because there is a higher ratio of hairs in the telogen phase than in the other areas of the scalp.
The duration of a telogen effluvium is variable, but rarely lasts more than a few months and there is invariably complete restitution unless another pathologic process also occurs.
As a rule, treatment is not necessary because the hair will grow back. For most patients, there is no evidence of residual loss of hair within a year. However, there have been cases of patients taking finasteride and reporting repeated bouts of excessive shedding. In this situation, it would be advisable to discontinue use of finasteride in favor of alternative anti-androgens.
