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How hair grows
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How hair grows
Overview
Overview
As there are three stages of hair growth, your head is never full of hair since there is always some hair in the resting stage of growth.
Structure of the hair and hair follicle.
The hair is constituted of the protein keratin. It has three layers an outer cuticle, middle cortex and central medulla. It also has a particular color which is the result of the presence of pigments - black and brown colors are determined by melanin, red and yellow by pheomelanin.
If the hair lacks these pigments, it will be is white. The scientific name for grey hair is Canites, but actually, grey hairs do not exist individually - it is just an illusion created by the blend of white and colored hairs.
Hair grows from a follicle, whose walls form its outer root sheath. In its lower part the follicle widens out and forms the hair bulb, which consists of the germinal matrix - the source of hair growth.
The hair situated in the follicle is encompassed by an inner root sheath which constitus of three layers. The rate at which the hair and the inner root sheath grow is one and the same, but at a certain moment the inner root sheath breaks down, so only the hair makes its way to the skin surface.
Hair Growth Cycle
Each hair follicle has a growth cycle. After the hair has grown to its maximum length, it ceases growing and is shed and substituted by another hair.
It is absolutely normal for people to have around 85% of their hair on their head, because the rest is in the resting stages.
Hair growth cycle can be divided into three major phases:
Anagen: the period during which a hair grows actively (takes about 1000 days or even longer)
Catagen: the period during which a hair breaks down and is shed (takes 10 days)
Telogen: the period of rest between hair shed and hair growth (takes 100 days)
Anagen The germinal matrix is formed by the epidermal cells encompassing the dermal papilla. Due to the constant division of cells, new ones are formed. The new cells push the older ones, and their shape begins to change as a result. Ones they reached one-third of their way up the follicle, the cells die. The average active growth period of a scalp hair is three years but it varies from one-and-a-half to seven years. A hair grows at an average rate of half an inch per month. Generally, around 85 % of the follicles are in this stage of hair growth.
Catagen This period indicates the end of the Anagen and is noted by changes taking place in the follicle. The hair stops growing and separates itself from the base of the follicle, forming a club hair. As a result of the breaking down of the hair bulb, the follicle shortens. A small part of the outer root sheath remains connected to the cells forming the papilla. The period of change lasts around three weeks. It has been estimated that 1% of the follicles are in the catagen stage.
Telogen The section of the remaining root sheath which is still in contact with the papilla is called the secondary or root germ. A new hair grows from this root germ. A follicle which has been changed and shortened does not produce a hair for about three months. 14% of the follicles are in the telogen stage.
