The reason for hair loss is a subject that no two doctors, scientist or clinics seem to be able to agree about, everyone seems to have their own opinion on the subject.

No two so called specialist hair clinics appear to agree on what actually causes hair loss. Indeed the medical profession themselves also have varying views on what the actual cause of hair loss really is, and how it should be treated. Rather than go for one view as to why hair loss occurs, listed below are a few reasons given by the various clinics as to their opinions on why hair loss occurs. This site is totally unbiased so it does not give only one company's opinion, it quote's most of them.
 

The general reasons for hair loss given by the medical profession, is as follows, probably in descending order.

Heredity factors

Ageing

Hormonal Imbalance

Illness and infectious diseases

Nervous disorders

Toxic substances

Injury and impairment

Severe radiation

Each of these problems can be a contributory factor towards hair loss, if there is a combination of two or more then the chances of hair loss are increased considerably.
 

Natural hair loss in a man, or male pattern baldness, as it is normally called is basically due to male hormones, (collectively known as Androgens). The most relevant of these hormones with regards to hair loss is called testosterone. In the case of a man who has inherited the necessary genes for hair loss, a little of this testosterone is formed by some of the hair roots into a derivative called Dihydrotestosterone. It is Dihydrotestosterone that is actually responsible for hair loss.

When anyone washes their hair there are always a few hairs left in the basin afterwards. This does not necessarily mean that the person is thinning. All that is happening is that some of the hair roots are shedding their old hairs and, in time, these will be replaced. The new hairs are as strong as the previous hairs were. The small white bobble on the end of the hair is not the hair root, it is in fact, formed from degenerated cells from within the hair root and is called the club. If it were possible for a hair to be pulled from the scalp bringing a hair root with it then the scalp would actually bleed.

If dihydrotestosterone has been produced it will be present in the surface sebum (grease) which is secreted by everyone from the sebum glands present through their skin tissue. Under these circumstances, when a hair is shed the dihydrotestosterone will enter the follicle (the hole in the scalp from which the hair has come) and inside there it reacts chemically. What it actually does is to miniaturise the hair root and follicle. This means that the new hair growing through will be finer. When this new fine hair is later shed the Dihydrotestosterone again miniaturises the follicle and hair root even further and hence the next hair will be finer still. This process will continue until the hair is so fine that it may as well not be there at all and if this happens over an area, then the man will obviously thin over that area and hence baldness occurs.

You can usually tell when a person is thinning on the front hair line by feeling the thickness of the hair and comparing it with the hair at the back of the head. It takes a bit of skill but eventually you should be able to tell just by touch when the hair is starting to thin.
 

One clinic in America claims that 99 per cent of all hair loss in men and women is caused by one thing - excessive oil. This oil, called sebum, clogs the pores of the scalp and stifles follicle growth. In time the hair root is asphyxiated, making it impossible for new hair to grow.

The follicles on top of a man's head grow straight up; consequently, when oil is released from the scalp, it has no place to go. On a woman's head, it can slip down the hair shaft towards the end, on a man's, it can only slide back to where it came from - the scalp.

If the scalp is not cleaned properly this oil becomes wax thus clogging the pores. When a hair is shed, its successor cannot come out. It becomes weak and literally goes to sleep under the scalp. The few hairs that manage to push through that waxy barrier are so puny that they are ready to fall out as soon as they break through. Such are the circumstances leading to Male Pattern Baldness.
 

Explanation Three

Baldness occurs not through heredity, nor as a result of the effects of testosterone on the hair follicles in the target zone. Rather it is caused because of: poor blood flow to the scalp (from a number of causes) insufficient nutrients in the blood and poor drainage of waste products through the lymphatic systems.
 

Men go bald because the hair is prevented from growing by being blocked at the hair growth centre - the hair follicle. What causes this blockage is the accumulation in the scalp, which some men are prone to, of dihydrotestosterone. This is the villain, not as is frequently thought testosterone. This accumulation of dihydrotestosterone may be the major reason for excess hair loss, combined with one or more other minor factors.
 

A co-operation of three factors brings about, especially in men, a typical hair deficiency in the area of the temples, a bald crown mid head or forehead area or a general thinning of these areas.

The three important factors for this development are as follows:

General disposition with a transmitted dominant tendency for male pattern baldness, female members of a family are transmitters as well.

Male Hormones (Androgen-Testosterone) are sponsoring male pattern baldness by means of increased production and a subsequent increase of Androgens in the blood stream thus increasing baldness.

As the period for hair loss is between the 20th and 50th years of age there is no danger of male pattern baldness before puberty.

Other factors such as mechanical irritation (washing, combing of hair, wearing a helmet, etc.) stress, lack of vitamins or minerals or undue influences of the weather are no cause, but only trigger male pattern baldness.

Through the already described genetic disposition, the hair growing Enzyme 5-Reductase is blocking the forehead, mid head and crown area, only the Donor areas at the back and on the sides of the head are not affected.

As scientists so far have not managed to influence the three factors above, and have not managed to arrest hair loss, not to mention growth of new hair, research tried to bring to the fore an attempt to activate the Enzyme 5-Reductase against the generic determination.
 

Conclusion

From the above it is obvious some explanations are plain and simple, though not necessarily correct, while others just become to technical for the average person.

As you can see there are many and varying explanations given for the cause of hair loss. Each clinic, consultant and even doctors will give different explanations for the cause of baldness as each person is trying to convince you that their products are the best on the market. Doctors who are not out to sell you anything do not usually see hair loss as a problem and are therefore not interested in giving you a reason for hair loss. Clinics have to sell to make a profit, so will try to convince you that their explanation is the real one and they just happen to have a cure for it.

I believe explanation one is the cause of hair loss.

The male hormone testosterone appears to be the main problem and is heavily linked to heredity.

The following is a list of drugs know to cause hair loss in certain cases:

Cholesterol-lowering drug:

clofibrate (Atromis-S) and gemfibrozil (Lopid)

Parkinson Medications:

levodopa (Dopar, Larodopa)

Ulcer drugs:

cimetidine (Tagamet), ranitidine (Zantac) and famotidine (Pepcid)

Anticoagulents:

Coumarin and Heparin

Agents for gout:

Allopurinol (Loporin, Zyloprim)

Antiarthritics:

penicillamine, auranofin (Ridaura), indomethacin (i\Indocin), naproxen (Naprosyn), sulindac (Clinoril), and methotrexate (Folex)

Drugs derived from vitamin-A:

isotretinoin (Accutane) and etretinate (Tegison)

Anticonvulsants for epilepsy:

trimethadione (Tridione)

Antidepressants:

tricyclics, amphetamines

Beta blocker drugs for high blood pressure:

atenolol (Tenormin), metoprolol (Lopressor), nadolol (Corgard), propranolol (Inderal) and timolol (Blocadren)

Antithyroid agents:

carbimazole, Iodine, thiocyanate, thiouracil

Others:

Blood thinners, male hormones (anabolic steroids)

If in doubt always ask your doctor to look up know side effects on any medication you are taking.