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There is much debate on this topic. While the link between certain forms of hair loss and the immune system is well-accepted, there is also evidence for a connection between the immune system and pattern loss (androgenic or androgenetic alopecia). In line with this, it appears that male hormones--especially DHT--trigger an autoimmune response in pattern loss, initiating an attack on the hair follicle that can be observed microscopically. This results in destructive inflammation that gradually destroys the follicle's ability to produce terminal hair. The reason for this could be that androgens somehow alter the follicle, causing it to be labeled as a foreign body. A possibly related factor is that elevated androgens also trigger increased sebum (oil) production, which can favor an excessive microbial and parasitic population, also leading to inflammation. In any case, hair progressively miniaturizes under the withering autoimmune attack, so that with each successive growth cycle it gets shorter and thinner until it finally turns into tiny unpigmented vellus hair (peach fuzz). In men, balding typically follows the classic horseshoe pattern known as male pattern baldness or MPB, though diffuse thinning can also occur. It has been noted that both the number of androgen receptors and the level of 5-alpha reductase, which converts testosterone to DHT, are higher in susceptible areas than in the rest of the scalp. Women's hair loss tends to be diffuse but is also primarily hormonally driven. The story of balding is, however, not the story of androgens alone. Rather male pattern hair loss appears to have multiple causes. For instance, damage to blood vessel linings can inhibit a growth factor they ordinarily produce: endothelium-derived relaxing factor (EDRF) or nitric oxide (NO). Minoxidil probably works in part by mimicking this growth factor. Similarly it has been noted that severe baldness is strongly correlated with heart disease and even diabetes, so there appears to be some common etiology outside of the strictly androgen paradigm for male pattern hair loss. There are likely othe
