Androgenetic alopecia, otherwise known as male pattern baldness, is hair loss due to both genetics and hormones that affects over 50% of males by the age of 50, and 80% by the age of 70. There is a misconception that male pattern baldness only comes from the maternal side of the family when in fact it originates from both the maternal and paternal side.
Genetics are mostly responsible for the whole process. Hair in the frontal scalp, temples, mid-scalp, and crown are genetically sensitive to the hormones (namely dihydrotestosterone or DHT) that cause the hairs to thin (miniaturize) and eventually go away. The first areas to be affected by male pattern baldness are the frontotemporal angles and vertex (crown). People state that they first noticed that hair was shedding in those areas. The process continues as the hairline recedes and the frontotemporal angles deepen. Eventually, the mid-scalp is affected, and if the process continues, the entire frontal scalp, mid-scalp, and crown will be mostly devoid of hair.
The most common system to define the state of hair loss is called the Hamilton-Norwood scale. This scale starts at a Norwood I which is just a small amount of frontal hairline recession to the Norwood VII which is almost completely bald except for a small rim of hair in the back of the scalp.
Hamilton-Norwood Scale
References:
Kelly Y, Blanco A, Tosti A. Androgenetic alopecia: an update of treatment options. Drugs 2016; 76: 1349–1364.
Otberg N, Finner AM, Shapiro J. Androgenetic alopecia. En- docrinol Metab Clin North Am 2007; 36: 379–398.
