Most men start to go bald in middle age, with about 80% of men having some hair loss by the age of 70. Male pattern baldness is the most common type of hair loss for men, the National Institute of Health said. Symptoms include a thinning of hair at the hairline, eventually creating a U-shaped or horseshoe pattern of hair on both sides of the head. The male sex hormone testosterone plays a key role, as do genetic factors. They cause the hair follicles to shrink, eventually becoming so small that they are invisible, leading to the appearance of baldness. While treatment is not necessary, side effects including psychological stress and loss of self-esteem due to change in appearance can be experienced.