On average there are around 70 thousands hairs on a person's head. They are distributed randomly on the scalp. It is normal for people to lose hair as part of a regeneration cycle that involves normal hair follicles.
Normally, the process of regeneration causes around 100 hairs to be lost daily. However, the lost hair will grow back again. In people suffering from hereditary hair loss, the fallen hair will not grow back. Thus less and less hair remains on the head. This process is medically termed androgenic alopecia (Baldness).
In addition, hair loss happens for other reasons, like stress, malnutrition and psychological factors. However, the sensitivity to testosterone byproducts remains the major reason for hair loss. When testosterone comes in contact with a specific enzyme, it is transformed into DHT (dihydrotestosterone) which in turn weakens the hair follicle and cuts off its nutrition and blood supply and consequently leads to hair thinning and loss.
Hair loss may cause psychological and emotional insecurity and may have serious implications on a person's life including loss of self esteem and feeling premature aging. Therefore, seeking a solution for hair loss is normal and essential.
In order to classify the pattern of hair loss, doctors created a series of charts categorizing various stages of hair loss.
The most commonly used chart for men is The Norwood/Hamilton scale shown below: