When blood levels of androgen decrease during puberty, patterned hair loss may begin its pattern. Commonly, the first sign of hair loss is a receding hair line, particularly in the temporal area. Hair loss is hereditary and usually begins to become apparent in men in their late 20's. In some men, it may not fully develop until their 40's or sometimes 50's. Still other men seem to avoid losing hair at all.

A main catalyst of hair loss is DHT, or dihydrotestosterone. DHT is a by-product of testosterone which develops sex characteristics in men while still in the embryonic period, and then later developing secondary sex characteristics during puberty. DHT characteristically attaches itself to the androgen receptors, fighting hair follicles and stunting its growth. Follicles affected by DHT shrink in size, usually to the size of follicles in an infant. DHT causes follicles to become thinner and shorter and eventually causes them to stop growing. Follicles will decay and the anagen, or growth phase becomes considerably shorter. The hair growth process usually takes as long as two to four years to complete itself. Once the anagen phase slows down, the hair loss process sets in and accelerates. Hair that continues to grow is usually noticeably finer and thinner.

This type of hair is referred to as baby hairs, or miniaturized hairs. The most common areas to be affected by pattern hair loss is the front or crown of the head. This pattern usually results in the U-shape common among balding men. It is interesting to note that the effects of thinning hair in men usually happen quicker than in women. This is because the levels of testosterone in men is much higher than women, so the hair shaft simply does not deteriorate as fast.

For many men, hair loss is inevitable. It is a hereditary condition that increases with age. These genes may be passed from either the maternal or paternal side.Other causes of hair loss include:

Stress – When you feel stressed out, your hair enters what is called a resting, or protective stage. Eliminating stress in your life will cause less hair to enter this state.

Dietary Imbalance – If you have poor eating habits, or a lack of protein in your diet, you can begin to see thinning hair. This is because protein is a major component of hair growth.

Changing hormonal balance and illness – Hormonal changes can cause cause hair fall, which is usually only temporary. Sudden illness can take it's toll on the body, causing the hair to enter the resting phase.