My understanding is that the reason people develop male pattern baldness is that the androgen DHT attaches to androgen receptors in the scalp, which kills the hair follices.
Generally the hair follices on the top of the head are more sensitive to DHT, which is why people go bald on the top of their heads but still tend to have lots of hair on the sides and back of their heads in a horseshoe pattern.
5-alpha reductase converts testosterone to DHT, and drugs that block the 5-alpha reductase enzyme are used to prevent and treat baldness.
My question is, do any of the other androgenic hormones cause male pattern baldness? What about synthetic androgens like the byproducts of anabolic steroids?
The chart I posted lists 5 naturally occurring androgens. Do all 5 cause male pattern baldness, or just DHT?
Why does it effect only the top of the head? I have a full beard but have not much hair on top for 50 years. More recently my hairy arms, legs and back have gone bald.
Testosterone, and to varying degrees other testerone-like compounds, are converted to DHT inside cell cytoplasm by a 5-alpha reductase (there are more than one form of this enzyme), which then binds to a sex hormone receptor in the cell nucleus forming a complex that impacts gene expression. Testosterone itself and the other analogs also directly binds to these receptors to various degrees. 5-alpha reductase levels and forms, and sex hormone receptor types and amounts, vary by cell type and location.
Scalp hair follicles both express a fair amount of 5-alpha reductase, and a sex hormone binding protein that binds to 5HT. So, @Hari_Seldon, the scalp pattern is due both to the individual cell expression of the enzyme converting the androgen into 5HT and the sensitivity of the cells by way of intranuclear sex hormone receptor expression, both type and amount, which is the sensitivity to 5HT. Other locations have different cellular expression of both, and presumably a different pattern of other cytoplasmic enzymes and intranuclear receptors.
The degrees to which any androgenic compound is acted upon by 5-alpha reductase vary, and so do their (weaker) ability to bind directly to the intranuclear sex hormone receptors. So how much balding they cause by that mechanism also varies.