Everyone sheds about 100 hairs a day, which is normal because each fallen hair is immediately replaced by a new one. The hair begins to thin when this hair regeneration process is not functioning properly and the speed at which the hair falls is exceeding the speed of the new hair growth.
There are four main theories that shed light onto the developments in human hair loss:
Evolutionary hypothesis
Despite a lack of general consensus on evolution of male hair loss, there is a hypothesis, proposed by several scientists, that suggests that male hair loss has evolved through sexual selection as a sign of aging and maturity, while things like risk-taking and aggression decrease in males with age. The aging and bolding male is in a higher social position and presents a lesser physical threat, allowing him to secure a partner and bring up his offspring.
Non-human hair loss
Hair loss is not an exclusively human feature. Other primates experience hair thinning and loss after adolescence. Some of these primates are even used in hair-growth treatment testing.
Genetics
A lot of research has been carried out to discover genetic causes in male hair loss and a suggestion is that it is mostly X-linked, however other genes unrelated to sex can also be involved. German academics identify the androgen receptor gene as the key condition for hair loss. They explain that a certain variant of it is required to prevent hair loss.
Other researchers name a different gene, also in the X chromosome as being responsible for male boldness.
Female hair loss
Female boldness is different from male one and should thus be addressed in a different way. First of all, it is less common for women to lose hair and the pattern in which this occurs is different. Usually, in women the frontal hairline is stable but the hair density decreases. The reasons of female hair loss are in contrast to male boldness, unrelated to the levels of testosterone. These reasons are however related to hormonal composition in a woman’s body. Women can notice hair loss in such conditions as pregnancy, a disease of ovarian cysts, menopause, contraception medication with high androgen levels, and polycystic ovary syndrome. Other conditions like anemia, thyroid gland disorders, chronic conditions and some drugs can also result in hair loss in women.
What causes hair loss?
To address the problem of hair loss in the most efficient way, and before taking medication like Propecia for it, you should devote considerable efforts to establishing the cause of hair loss. Various things can cause hair loss, some of them resulting in short-term hair loss, such as stress of a long-lasting illness, others bringing a long-term effect, like hormonal problems, often related to thyroid gland disorders.
Some medications can also cause hair loss and this effect may be reversed if you stop taking such medication. There are some infections that affect hair growth as well; so addressing these infections will prevent hair loss. Boldness can also be related to some underlying disease like diabetes and treating the disease is the most correct way to address hair loss.