subject: Causes of Hair Loss [print this page] Causes of Hair Loss Causes of Hair Loss
What causes hair loss?
A: 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 other factors as well.
What is DHT?
A: Dihydrotestosterone (DHT) is produced from the male hormone testosterone by the enzyme 5-alpha reductase. DHT is the androgen thought to be most responsible for the type of hair loss also known as male pattern baldness. DHT has a very high affinity for the androgen receptor and is estimated to be five to ten times more potent than testosterone. Other androgens that may be significant in pattern loss include androstenedione, androstanedione and DHEA (especially in women). All of these fall into hormonal pathways that can potentially result in elevation of DHT downstream via various enzymes. It is possible that certain DHT metabolites may play a role in male pattern hair loss as well.
Is stress a factor in hair loss?
A: Sometimes stress can play a role in diffuse loss. Stress-induced loss ordinarily regrows within a year of eliminating the cause.
