This is the most common type of hair loss in men. It affects approximately 50% by age 50. It is characterized by progressive loss of hair in a certain pattern. The typical site of involvement are: the front of the scalp, mid scalp, side of the scalp and the vertex. This is otherwise known as male balding or male pattern hair loss.
This is more common in Caucasians and less so in Asian or African-American men. A family history is often present, but a negative history does not exclude this. It is due to both hormonal and genetic factors. The growth phase of the hair is typically shortened and there becomes a shift in the growth vs resting phase of the hair cycle. Follicles undergo miniaturization and coverage of the scalp decreases.
The key androgen involved in the induction and promotion of male pattern baldness is Dihydrotestosterone (DHT). DHT is a metabolite of Testosterone and has a greater affinity for the androgen receptor. The enzyme 5 -alpha-reductase converts Testosterone to DHT. DHT binds to the receptors at the cellular level and activates genes which transform large follicles to smaller follicles and shorter growth phases.
Androgenetic Alopecia is seen by different degrees of hair thinning and nonscarring hair loss. This is a continuous process which progresses over time. It comes in waves with some men noticing it at more rapid intervals.