alopecia
Meaning of alopecia: The pattern of loss, and whether the follicle survives, matter more than the amount, because one determines whether hair can return.
Definition of alopecia
Alopecia is the medical term for hair loss: the partial or complete absence of hair from areas where it normally grows. It may involve the scalp alone or hair across the whole body, and it can come on gradually over years or within weeks. The word describes the finding rather than any single cause.
How does hair growth work?
Each follicle cycles independently through a long growing phase, a brief transition and a resting phase, after which the hair is shed and a new one begins. Shedding a modest number of hairs daily is normal because follicles are not synchronized. Hair loss becomes visible when many follicles are pushed into resting at once, when the growing phase shortens so that hairs are replaced by finer ones, or when the follicle is destroyed. A treatment such as chemotherapy acts on the first mechanism differently again, striking cells that are actively dividing in the follicle so the growing hair breaks off at the scalp.
What are the main types?
| Type | Pattern | Follicle |
|---|---|---|
| Androgenetic | Gradual thinning at the crown and temples, or diffusely | Shrinks over time, hairs get finer |
| Alopecia areata | Round smooth patches, sometimes total loss | Preserved; regrowth is possible |
| Telogen effluvium | Diffuse shedding after illness, childbirth, surgery or major stress | Preserved; usually recovers |
| Anagen effluvium | Rapid, widespread loss during chemotherapy | Preserved; regrowth expected after treatment |
| Traction | Loss along the hairline from prolonged pulling by tight styles | Recoverable early, scarring if prolonged |
| Scarring | Patches of smooth skin with no visible follicle openings | Destroyed; loss is permanent |
Why does the cause change what happens next?
The dividing question is whether the follicle survives. Where it does, hair can return once the trigger passes, though texture and color may differ from before. Where inflammation has destroyed it and replaced it with scar tissue, the loss is permanent, which is why scarring types are distinguished early. In alopecia areata the immune system attacks the follicle without destroying it, so patches can regrow and then recur unpredictably. Androgenetic thinning reflects a genetic sensitivity of the follicle to androgens and progresses slowly. Thyroid disease, iron deficiency, some medicines and scalp infections can each produce hair loss, and the distribution across the scalp is the main clue to which process is at work.
Also known as
Used in a sentence
The patient was counseled about expected alopecia as a side effect of the planned chemotherapy regimen.
Good to know
Hair loss from chemotherapy or from a temporary shedding phase generally reverses once the cause passes, whereas scarring alopecia destroys the follicle and the loss is permanent, which is why the type rather than the extent determines whether regrowth is possible.
Word origin
Where “alopecia” comes from
From Greek alopekia, from alopex, meaning fox, an old reference to patchy hair loss resembling the mange seen in foxes.