reasons of hair loss

The followings may be mentioned as the reasons of hair loss:
Different kinds of malnutrition including severe weight loss related to nonstandard diets, in which weight loss occurs (more than 2 to 3 kilograms a month)
 nutritional deficiencies such as iron, zinc and vitamin deficiencies
severe bleeding
hyperthyroidism and hypothyroidism
post parturition and post surgery alopecia
nutritional deficiencies induced chronic diarrhea
severe febrile illnesses  
some drug consumptions
mental and nervous breakdown
severe fears, etc.