Authentic and factual Hair loss reasons:

The amount of hair remains constant from birth to death and it has nothing to do with the nutrition, life style, vitamin taking or diet, while the hair thickness changes in different life stage and race. At the puberty ages the hair line gradually recedes over time, and at 40 often progressing to partial or complete baldness.
The main reason for hair loss contains a variety of genetic and environmental factors such as:

•Genetic factors
•Stress
•Age
•Hormones

Genetic factors:

The main role of DNA molecules is the long-term storage of information.
The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.
DNA is organized into structures called chromosomes.
These chromosomes are duplicated before cells divide, in a process called DNA replication. Chromosomes are inherited both from the paternal and maternal grandparents they are 46.
The genetic component of male pattern baldness, is androgenetic alopecia, research indicates that susceptibility to premature male
pattern baldness is largely X-linked and the importance of the maternal line in the inheritance of male pattern baldness is more apparent. While hormones and other factors can also effect and cause baldness. Though scientists are pretty close to identifying the genes responsible for baldness, the actual process of baldness is still quite a mystery.

Hormones:

Hormones are chemicals released by cells and affect cells in other parts of the body, hormone molecules are usually released directly into the bloodstream, flow from cell to cell by diffusion in a process known as paracrine signaling.
The male hormones are generally called Androgens that are important for normal male sexual development before birth and during puberty.
Androgens also have other important functions in both males and females, such as regulating hair growth and sex drive. Hair loss in men with androgenic alopecia is typically related to hormones called androgens, particularly an androgen called dihydrotestosterone (DHT).
From decades ago the relation between baldness and tesis was explicit, in the oriental polygyny societies when the king had Harems for their wife's, it was noticed that the castrated Harem servants did not receive alopecia.
In the early 20 century psychopaths used to be castrated because it was though the sexual hormones is the main reason for their psychopathy.
When a psychopath twin was castrated due psychopathy, it was noticed that he did not received baldness while his identical twin brother was affected.
The doctors then injected the Testosterone to the castrated twine and noticed his gradual hair loss so they came to conclusion that the hormones mainly created in prostate are responsible for baldness. Nowadays, DHT is one of the major hormonal causes of baldness, it is a form of testosterone converted to its state by an enzyme created in the prostate, and this testosterone causes hair follicles die and shortens the hair follicles growing cycles, and causes the hair grown to be weaker.

Age:

Age can be considered as one of the main reasons for the hair loss, over time the hormones affect the hair follicles and cause hair loss. Although age can affect the hair growth, the genetic background and the hormones affect the hair loss procedure too. It is noticed that the male pattern baldness has a cyclic nature and the main reason is still a mystery.

Stress:

Stress can also be another reason for hair loss. Emotional or physiological stressful events can result in an alteration of the normal hair cycle with causes including fever, childbirth, and chronic illness. Scientifically, this is a different problem comparing gradual genetic hair thinning or male pattern baldness simply because the hair loss will be recovered while in the male pattern baldness this is not the case.