What is hair loss?
Hair loss and baldness are common problems. There are various forms and causes of hair loss; the most common are discussed here.
How does hair grow?
Hairs are produced in the hair follicles. The number of hair follicles on the scalp is around 100,000. This differs for each individual and is genetically determined; blonde people, for example, have more follicles than people with reddish or black hair. Hair growth has several phases: the growth phase (anagen), the transition phase (catagen) and the resting phase (telogen). The growth phase of scalp hair lasts on average about 3 years, and is longer in women than in men. During the last year of growth, cell division slowly decreases and the base of the hair becomes thinner. Then the transition phase begins, in which growth stops completely and the hair is less firmly anchored. In the resting phase that follows, the hair falls out; after a few months the follicle redevelops and a new hair is produced. Over life the number of follicles (and so the thickness of the hair) decreases, partly depending on hormonal factors.
Types of hair loss
Androgenetic alopecia (male/female pattern)
This is a very common form of permanent hair loss. In men it is completely normal and in women it is only rarely a sign of an underlying disease. In men with a predisposition, the hair loss begins at some point after puberty, with very gradual loss on the crown and at the temples that slowly spreads, while the hair at the sides and back is not lost. This is due to an inherited sensitivity of the hair to dihydrotestosterone (DHT), one of the male hormones, which shortens the growth phase so the hair looks thinner and eventually the roots shrivel. In women, female-pattern hair loss is common around the menopause, concentrated mainly on the crown; the extent is often hereditary. When androgenetic-type complaints arise in young women, the doctor will often investigate hormonal (endocrine) causes.
Alopecia areata
Here there is patchy hair loss, usually on the scalp, but in principle it can affect any hairy area, such as the beard, pubic region and eyebrows. In 5–10% of patients all scalp hair falls out (alopecia areata totalis), and in 1–2% all body hair is lost (alopecia areata universalis). Alopecia areata is almost certainly an autoimmune condition, in which the body wrongly recognises the hairs as foreign and rejects them; under the microscope an inflammatory reaction can indeed be shown around the follicles. It has an unpredictable course; in most people the hair falls out suddenly in patches and regrows on its own within 2 years.
Telogen effluvium
When an unusually large number of hairs enter the resting (telogen) phase at the same time, many hairs fall out, usually diffusely across the scalp. The person notices relatively a lot of hair falling out — on the pillow, in the shower drain. This “synchronisation” of the growth phases can usually be traced to a stressful event 2 to 4 months before the hair loss began, such as pregnancy, a feverish illness or severe mental stress. Growth usually recovers within a year, though unfortunately not always completely, and no treatment is known to speed recovery.
Drug-induced hair loss
Medicines can also cause hair loss, diffusely over the scalp. Well known is the extreme hair loss from certain forms of chemotherapy, but other medicines can also be responsible. Drug groups that fairly regularly cause problems include cytostatics (chemotherapy) very often; anticoagulants (“blood thinners”), retinoids (isotretinoin, acitretin) and lithium regularly; and antimalarials, beta-blockers and ACE inhibitors sometimes.
Scarring (cicatricial) hair loss
When the skin scars, the follicles disappear and no hair can grow there again, even after the original condition heals. Causes include certain inherited conditions; infections (bacteria such as syphilis, fungi, protozoa); cancers (basal cell carcinoma, squamous cell carcinoma, lymphomas); physical causes (radiation, burns); and inflammatory skin conditions (lupus erythematosus, lichen planus, sarcoidosis, frontal fibrosing alopecia, folliculitis decalvans, and others).
Hair loss from internal conditions
Various internal diseases can cause hair loss. An important example is thyroid problems, which can cause diffuse hair loss and partial loss of the eyebrow hairs (with an underactive thyroid). Conditions in which too few nutrients are absorbed from the digestive tract (malabsorption syndromes, such as gluten enteropathy) can also cause hair loss.
Other causes
Smoking is reported to raise the risk of hair loss, explained by reduced blood flow to the skin, so less oxygen and nutrition reach the roots. Trichotillomania is hair loss from repeated pulling at the hairs by the person themselves, often unconsciously, giving a fairly sharply bordered bald or sparse patch; stopping the manipulation usually leads to full recovery. Traction alopecia results from hairstyles with continuous pull (tight braids, tightly tied ponytails); prolonged traction can make the loss permanent. Loose anagen hair syndrome is a thinning seen mainly in young children (especially girls).
When to see a doctor
See a doctor if hair loss is sudden, patchy, rapid or extensive, if the scalp is red, scaly or scarred, if eyebrows or eyelashes are affected, or if hair loss comes with other symptoms (such as fatigue or thyroid complaints), so the cause can be identified.