Hair loss: Why hair falls out?

The life cycle of the hair provides the alternation of three phases, one of growth, rest, and a drop.  The average duration of this cycle varies from 2 to 7 years.  It is estimated that each follicle produces about 20 hairs in the course of his life.
The number of hair fell during the day is variable and depends on many factors such as:
Sex (the fall is greater in men than women)
The season (in autumn and spring-fall increases)
Health conditions (the use of certain medications and some diseases can accelerate the fall)
Washing and brushing (mechanical trauma facilitates the posting of hair)
Density of hair (more hair you have, the greater the fall in absolute terms)
Genetics (some people are genetically predisposed to the fall).
For information only, without such a rule is given, a fall of over 100 hairs a day continued for several weeks is a sign of suffering hair.  In these cases you should contact a physician can assess and resolve the situation