Hair Growth Cycle.
Updated: Jul 8, 2019
Did you know each hair on our head has a life cycle and that each hair falls out naturally after a certain period? In order to take good care of hair, we need to understand the natural growth cycle of hair and this article explains the same in detail.
By week 22, a developing fetus has all of its hair follicles formed. At this stage of life there are about 5 million hair follicles on the body. There are a total of one million on the head, with one hundred thousand of those follicles residing on the scalp. This is the largest number of hair follicles a human will ever have, since we do not generate new hair follicles anytime during the course of our lives.
Most people will notice that the density of scalp hair is reduced as they grow from childhood to adulthood. The reason: Our scalps expand as we grow.
Hair is simple in structure, but has important functions in social functioning. Hair is made of a tough protein called keratin. A hair follicle anchors each hair into the skin. The hair bulb forms the base of the hair follicle. In the hair bulb, living cells divide and grow to build the hair shaft. Blood vessels nourish the cells in the hair bulb, and deliver hormones that modify hair growth and structure at different times of life.
Head is made up of about 150,000 hair follicles. Around 80-90% of hair is in the anagen, or growing, phase of the hair growth cycle at any one time. Throughout the cycle, the hairs on your head are in various stages of growth and shedding.
Hair grows from the follicle, or root, underneath the skin. During our lifetime, we have about 25-30 hair-growth cycles. It is important to note that the total number of hair usually remains constant, in spite hair going through different phases. Ideally the ratio between Anagen and the Telogen phase known as A/T ratio is usually 80:20. This means 80% of the hair is in growing phase and 20% are in the falling phase. Hair growth is also affected by seasonal changes. For instance, hair grows more quickly in summer than in winter and falls more in autumn than other seasons. The growth rate of hair also tends to slow down with ageing. The hair can grow to maximum length of 36 inches in women. It is rare to find hair exceeding 36 inches.
The hair growth may be affected by hormonal changes in body. In men, the male hormone androgen destroys the hair follicles and thus raises the risk of hair thinning or balding in men. In women, the balding is rare because of the protective action of estrogen towards the hair. However, in periods where estrogen levels fall, androgen can affect the hair follicle in women too. This happens in life stages such as menopause or even after delivering a baby.
The hair is ‘fed’ by blood vessels at the base of the follicle, which give it the nourishment it needs to grow.
Between starting to grow and falling out years later, each hair passes through four stages:
ANAGEN, CATAGEN, TELOGEN and EXOGEN. Every hair is at a different stage of the growth cycle.
1. ANAGEN (GROWING PHASE) The anagen, or growing, phase usually lasts 2-7 years, and the length of this phase determines the length of our hair.
2. CATAGEN (TRANSITION PHASE) This is the transitional phase that lasts about ten days. During this stage, the hair follicle decreases in size and detaches from the dermal papilla.
3. TELOGEN (RESTING PHASE) This is the telogen, or resting, phase, which generally lasts around 3 months. Around 10-15% of the hair on your head is in this phase at any given time. While the old hair is resting, a new hair begins the growing phase.
4. EXOGEN (SHEDDING PHASE) This is a part of the resting phase where the old hair detaches and sheds, and new hair continues to grow. Approximately 50 to 150 of your hairs may fall out daily. That is considered a normal rate of hair shedding. Hair growth and hair shedding is impacted by a number of factors, including everyday stress, medication, age, heredity and damage caused by the environment, overstyling and poor nutrition.