Reason for hair fall

The general reasons for hair loss given by the medical profession, is as follows, probably in descending order.
Heredity factors
Ageing
Hormonal Imbalance
Illness and infectious diseases
Nervous disorders
Toxic substances
Injury and impairment
Severe radiation
Each of these problems can be a contributory factor towards hair loss, if there is a combination of two or more then the chances of hair loss are increased considerably.