Man with a receding hairline.
© Science Museum / Science & Society Picture Library
Hairlos is caused by heredity, hormones, and age. Most hairlos is caused by androgenic alopecia which can be inherited from either the mother's or father's side of the family. Although women can carry a gene for baldnes, they don't usually go bald because their female hormones protect them. However, they can pas on the gene to their male children. It is therefore posible for a man with a full head of hair to have a son whose hairline is receding. The other main cause of baldnes is over-production of the male hormone dihydrotestosterone (DHT). Testosterone is converted into DHT by enzymes produced in the prostate, adrenal glands and scalp. Too much DHT causes the hair follicle to shrink so that the hair becomes very fine and eventually falls out.