There are many ideas on why hair loss occurs and it would seem that everyone you talk to has a reason for why it may be happening to you. There are of course only a few scientific proven reasons for hair loss and many of the other reasons are just merely old wives' tales. The five most common reasons for hair loss are:
The major cause of hair loss is DHT. DHT is a hormone. DHT is directly related to and affected by the level of testosterone in the bloodstream. DHT blocks the growth of hair in men and is the cause of most baldness. And even though this is a male hormone, women also have a small amount that runs through their blood, some higher than others. When a female inherits hair follicles that are supersensitive to DHT, they start to lose hair just like men do. Men generally have hair loss concentrated in a specific pattern from the front through to the crown, while women have an overall thinning of the hair throughout the scalp. About half of all people have inherited hair loss by about 50 years of age.
Although not the primary cause of male-pattern hair loss, genetics does have a significant role in male-pattern hair loss. It is unclear whether having an affected mother or an affected father predisposes descendants to greater risks. When hair loss is related to hormones (androgens) and genetics, it is known as Androgenetic Alopecia, or more commonly just balding. Androgenetic Alopecia is an extremely common disorder.
3. Poor Blood Circulation
Hair loss can be attributed to overall poor blood circulation. Studies have shown that the blood flow to the scalp of men and women suffering from hair loss was significantly lower than those not experiencing hair loss.
4. Environmental Pollutants.
Further studies have indicated that pollutants in the atmosphere have contributed to the production of "environmental hormones" which can also contribute to hair loss.
SUMMARY: As you can see there are many factors that can cause hair loss in both men and women but they all have one underlying theme in common, hair follicles that are affected by hormonal "clogging" agents and poor blood and nutrient circulation are less likely to experience a healthy growth cycle.