Human hair is a keratinised structure that goes through three stages of normal development (hair cycle):
Anagen phase (or growth phase)
Which lasts between two and six years. The hair emerges and grows one centimetre per month on average. The follicle is always active. A total of 90% of the hair on your head is in this phase.
Catagen phase (or resting)
Is a stable phase that usually lasts about three weeks. Hair stops growing and falls out of the papilla.
Telogen phase (or fall)
In this phase, the follicle rests and hair starts to fall out. This takes around 2-5 months.
Basically, hair follicles contain the hair, which is a keratinised structure emerging from an epidermal invagination. It is deep inside (dermal papilla), where it receives the cellular nutrition. The content excreted by the glands empties into the follicular infundibulum:
Control temperature, excrete water and other substances (salt, ammonia, uric acid, urea, lactic acid). These glands also produce odours, secreting a substance that quickly becomes contaminated and generates the familiar body odour.
Produce lipids that help to maintain the protective layer.
Each hair grows from a follicle and each follicle has its own cycle, which is independent from those surrounding it. That is why each hair on your head is in a different phase of its life cycle, at any given time. There are between 100,000 and 150,000 hairs on the head of a person without alopecia, of which 85%-90% are in the anagen phase or growth period, 1-2 % in the catagen or resting phase, while 13-14 % are in the telogen or fall phase.
OF THE HAIR IS IN THE ANAGEN (GROWTH) PHASE
OF THE HAIR IS IN THE TELOGEN (SHEDDING) PHASE
OF THE HAIR IS IN THE CATAGEN (REST) PHASE
We know that for every 100 hairs that we have, there is always one in the 12-15 % replacement phase and it can take around four years to completely renew all our hair.
On average, in one day around 70-100 hairs are lost. In normal conditions, these are replaced by new ones generated by the hair follicle.
Eight in ten people who believe that they have alopecia,do notpathological substrate. All that is happening is that we are losing hair randomly and this is not replaced immediately. Therefore, the concept is based on renewal of the hair follicles rather than hair loss. This process, called telogen effluvium, is often seasonal and depends on various factors (the environment or food).
However, there are also genetic factors that affect the speed at which the renewal process occurs, which means that hair falls out at a different speed to the natural renewal process.
Reversible and not localised in a certain portion of the scalp.
Causes circular bald patches and is usually reversible.
Caused by trauma or pressure. It is also caused by trichotillomania which is the nervous habit of hair pulling.
This type of alopecia destroys the hair follicle. Hair loss is irreversible: