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Ethnic background : The appearance of hair and growth are not the same for Asians, Black people or causasians. For example, Asians have a longer anagen phase.
Age : in a growing child, the number of anagens is at its peak. From puberty onwards it starts to diminish and between the age of 15 and 65, we lose 1/3 (one third) of our hair. This means that after 65, the number of anagens drops significantly.
Food : clinical experiments have shown that malnutrition may be the cause of hair loss and short or non-existant anagen cycles.Studies conducted have highlighted the importance of sulpered amino acids (cysteine-methionine) present in proteins ; vitamins : vitamins A, C, and especially B and H.; also indispensable minerals, like zinc, copper and iron.
Essential fatty acids, for example, linoleic acids, necessary for good hair trophicity.
Hormonal factors, We suspect hormones have an affect on the hair cycle because we know that men who have been castrated have increased hair growth. The introduction of male hormones can lead to hair loss. These results were discovered following experiments on humans and animals.
The hormone mechanism works as follows : the endocrine gland secretes a hormonal substance that is released into the blood. This fixes on to the target cells, those of the hair roots. There are receptors on the surface of the cells that capture the hormone and when the hormone receptor block becomes a whole, it starts off an "information" reaction which is sent via a protein in the middle of the cell which modifies it's behaviour.
The most important changes are carried out by the sex hormonees, especially the androgens or male hormones. These hormones are turned into dihydrotestosterone, via an enzyme called alpha-reductase 5. This dihydrotestosterone is made up of the carrier terminal that will meet the receptors of the cell wall of the hair root cells.Better knowledge of this alpha-reductase 5, as well as the receptors, has allowed significant progress to be made in treating androgenic alopecia in man.
The female hormones, oestrogen and progesterone have a lesser effect.
Thyroid hormones, expecially in the case of hyperthyroidism, and hypophyseal hormones and sometimes panhypopituitarism, can sometimes play a role in the modification of hair cycles. Luckily, these illnesses are rare.
The immune system : Experiments have proven that it has a considerable effect in certain pathologies, for example, alopecia. However, it's precise place in the hair cycle is difficult to pinpoint.
