Each hair follicle on the scalp grows for 2-8 years before entering the regression phase, resting and falling out and then returning to the beginning of the cycle.
Hair follicles are small tubes that contain the hair root, where hair grows. Hair follicles develop mainly in the top two layers of the skin. They connect to blood vessels at the rounded base of the root called the dermal papilla. This papilla sends signals about the growth as well as the color and size of the hair strands. Each hair follicle goes through about 10-30 hair growth cycles throughout its life.
Each cycle consists of 4 phases including anagen (growth phase), catagen (regression phase), telogen (resting phase) and exogen (shedding phase).
Anagen phase
This is the hair growth stage. The base of the hair follicle expands and then becomes the hair shaft. Each strand of hair grows from the root and grows through the hole at the tip of the hair follicle. Before entering the anagen phase, hair follicles produce cells that later form hair. When hair reaches the surface of the skin, it is in the metanagen phase.
The anagen phase usually lasts 2-8 years for each hair follicle. About 90% of hair follicles on the scalp are in this stage at any given time in life. Hair grows at a rate of about 1/3 of a millimeter per day or about 15 cm per year.
Catagen phase
This is the transition from growing hair to the third stage, lasting about two weeks. At this time, the hair follicle becomes a little smaller and separates from the hair papilla.
Telogen phase
The telogen phase is a resting phase, when hair does not grow and hair follicles are in a dormant state. About 10-15% of the hair on the body is in the resting phase, which usually lasts for several months.
Exogen phase
At this stage, hair falls out of the scalp, is pushed out as new strands emerge from the hair follicles, and as the anagen phase begins again. About 100-150 hair follicles fall out each day, the amount varies from person to person.
Hair grows at a rate of about 1/3 of a millimeter per day or about 15 cm per year. Image: Ngoc Pham
If the above hair growth cycle is interrupted, hair may begin to fall out faster than it grows back, leading to thinning hair, a receding hairline or alopecia areata. There are many factors that can disrupt the hair growth cycle including:
– Imbalance of thyroid or other hormones.
– Inflammatory condition.
– Stress.
– Genetics.
– Lose weight quickly.
– Giving birth.
– Surgery.
– Autoimmune conditions such as psoriasis, lupus or autoimmune thyroid disease.
– Nutritional deficiencies include vitamin D, iron and protein.
Taking certain medications and medical treatments such as chemotherapy.
To promote healthy hair growth, each person should provide enough nutrients such as iron, vitamins C and D through diet and supplements if needed. Choose a shampoo suitable for your hair type, wash your hair more often if your hair is oily, maximum once a day. Focus on applying shampoo to your scalp, where oil and dirt accumulate. Use conditioner on the ends of your hair to strengthen it and help protect it from ultraviolet (UV) rays from the sun. Protect your hair when swimming to avoid exposure to toxic chemicals.