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Hair cycle of growth and rest
Like your skin and nails, your hair goes through a finely tuned cycle of growth and rest. There are 3 phases in a hair cycle:
- In the first stage, your scalp hair is continually growing. During this anagen phase, your hair grows about 1–2cm per month. About 90% of your hair is in this stage at any one time. It lasts between 2–5 years.
- The second stage, called the catagen phase, is when growth stops. About 1–3% of your scalp hair is in this phase at any one time. It lasts for 2–3 weeks.
- The third stage, the telogen phase, is a resting phase that lasts between 1–4 months. About 10% of your scalp hair is in this phase at any one time.
Hair shedding phase
At the end of its resting stage, your hair goes through a shedding phase, which normally results in growth of new hair. When a hair is shed, it’s replaced by a new hair from the same hair follicle located just beneath the skin surface. Of the 100,000 hairs on your body, you may lose 50–100 every day, while what is lost is replaced.
Disturbances to any phases of the hair cycle can cause abnormal hair loss.
Possible causes of abnormal hair loss include:
- alopecia areata (an autoimmune condition affecting the hair follicles)
- telogen hair loss (excessive hair shedding)
- anagen hair loss (decreased hair growth)
- trichotillomania (hair-pulling disorder)
- skin conditions
- traumatic hair loss
- radiation therapy
- medication – a large number of medicines prescribed may influence hair growth, including those for cancer, depression, arthritis, gout and high blood pressure as well as blood-thinners.
Alopecia areata is an autoimmune disease, in which your immune system mistakenly assumes your skin is foreign and creates antibodies that attack your hair follicles, causing them to shrink and stop producing hair.
This condition causes your hair to fall out abruptly, resulting in totally smooth, round patches about the size of a coin, or larger, on your scalp. The condition may run in families and can affect children and adults of any age, commonly affecting those under the age of 20.
Severe stress is a possible cause of alopecia areata, but this is difficult to prove. It is not unusual for this condition to either stop suddenly or last for months or years. Nails can also be affected in some people, with pitting or fracturing.
There are a number of autoimmune diseases, and women are twice as likely as men to have one. Read more about autoimmune diseases.
Telogen hair loss
Telogen hair loss, also known as telogen effluvium, is a condition in which you shed too many hairs. Many of your hairs have been pushed into the resting (telogen) phase, causing excessive shedding. This may lead to losing up to 500 hairs a day.
You may realise you’re shedding more hair than usual or handfuls of hair can be found on your pillow, comb, hairbrush or in the plughole. Causes include:
- fever or severe infection
- thyroid disease
- low iron
- weight loss and malnutrition
- excessive bleeding
- major surgery or chronic illness (with a period of up to 3–4 months before you see the hair loss)
- stress, eg, a major life event in the family
- low protein intake or a rapid weight loss diet
- low zinc intake
- medicines such as contraceptives, anticoagulants and anticonvulsants.
Anagen hair loss
Anagen hair loss, also known as anagen effluvium, is when your hair is held in the growing (anagen) phase. Your hair can’t grow longer and is broken. Your hair loss is sudden and can be caused by the following factors:
- cancer treatment such as chemotherapy, radiotherapy or medicines that can suppress your immune system
- short anagen syndrome – an inherited condition in which children can’t grow their hair long.
If you have anagen hair loss caused by medicines, hair growth will resume when the medicine is stopped.
Trichotillomania, also known as hair-pulling disorder, is a behavioural disorder that mainly affects adolescents. It can be associated with other mental health conditions such as obsessive compulsive disorder, depression or anxiety. This condition causes recurrent urges to pull your hair, which leads to hair loss.
Skin conditions that affect your scalp can also cause hair loss. Examples include:
- seborrheic dermatitis, eg, dandruff
- lichen planus
- discoid lupus erythematosus
- tinea capitis – a fungal infection of your scalp
- impetigo (school sores) – a bacterial skin infection.
If you have a skin condition causing hair loss, you may have other skin symptoms such as skin redness, rashes, scarring or itchiness.
Traumatic hair loss
Traumatic hair loss or traumatic alopecia (also known as traction alopecia) may be due to the use of hair reshaping products (relaxers, straighteners, hot combs) or the persistent physical stress involved with tight rollers and tight braiding. Using these styling methods over a long period of time can lead to irreversible hair loss (your hair won’t grow back). If you have hair loss, stop these hair styling practices.
While hair dyes (that contain paradye) may cause scalp irritation, hair loss is uncommon from that cause.