Hair Growth Cycle: How Hair Grows and Sheds

The hair growth cycle explains many things that puzzle people about their hair: why some shedding is normal, why hair loss shows up months after an illness, and why no product can make hair grow overnight. Every hair on your head follows the same repeating cycle, each on its own schedule.

Hair basics

• The scalp has roughly 100,000 hair follicles.
• The follicle, under the skin, is the living part that makes the hair.
• The hair shaft, the part you see, is made of the protein keratin and is not alive.
• Scalp hair grows about one centimeter a month, or around 12 to 15 cm a year, with individual variation.

The phases of the cycle

Anagen: the growing phase

The length of this phase decides how long your hair can grow. Someone with a seven-year growing phase can grow hair past the waist. Someone with a two-year phase will find that hair stops at the shoulders. This is set largely by genes.

Catagen: the transition phase

The follicle detaches from its blood supply and moves upward. The hair becomes a "club hair" with a small, pale bulb at its end.

Telogen: the resting phase

The club hair sits in the follicle for about three months while a new hair begins to form beneath it.

Exogen: the shedding phase

The old hair falls out, often during washing or brushing. This is why you lose about 50 to 100 hairs a day.

Why you do not go bald between cycles

Each follicle runs on its own schedule. At any moment most hairs are growing while a few are resting or shedding. Many animals moult in seasons because their follicles cycle together. Human scalp hair does not.

What disturbs the cycle

• A shock to the body. Illness, surgery, childbirth or rapid weight loss can push many hairs into the resting phase at once. They shed two to three months later. See Stress and Hair Loss: Understanding Telogen Effluvium.
• Hormones. In hereditary hair loss, the growing phase becomes shorter and the follicles smaller, so hairs become finer and shorter with each cycle.
• Nutrition. Shortages of protein, iron and other nutrients interrupt growth. See Nutrition and Hair Health: Nutrients Your Hair Needs.
• Medicines and medical treatment. Some medicines affect the cycle. Chemotherapy stops dividing cells and causes rapid loss of growing hairs.
• Age. Growth slows and hairs become finer.

Why results take months

Because the resting phase lasts about three months, the effects of any change, good or bad, appear after a delay. A treatment for hair loss usually needs at least three to six months before it can be judged. The same delay explains why shedding seems to arrive "from nowhere".

Can you speed up growth?

The growth rate is mostly fixed by your genes, age and health. You cannot make follicles work faster with a shampoo or an oil. What you can do is:

• Keep the hair you grow by preventing breakage.
• Eat a balanced diet.
• Look after your scalp.
• Seek treatment early for conditions that shorten the growing phase.

Tracking your own growth

Measuring a section of hair once a month shows your personal growth rate and whether breakage is taking the length away. The Hair Length Tracker keeps a record of your measurements.

Body hair is different

Eyebrows, eyelashes and body hair have a much shorter growing phase, a few weeks to months, which is why they stay short.

For the difference between normal shedding and breakage, see Hair Shedding vs Breakage: Key Differences. For causes of thinning, see Hair Thinning: Causes and When to Get Help.

Related on ArniSun

• Hair Shedding vs Breakage: Key Differences
• Stress and Hair Loss: Understanding Telogen Effluvium
• Hair Thinning: Causes and When to Get Help
• Nutrition and Hair Health: Nutrients Your Hair Needs
• Hair Length Tracker: Record Your Hair Measurements

Sources and further reading

• DermNet: Hair loss
• DermNet: Telogen effluvium
• American Academy of Dermatology: Do you have hair loss or hair shedding?