Alopecia areata
Autoimmune disorder causing patchy hair loss on scalp and body.
Alopecia areata, sometimes called spot baldness, causes hair loss on the scalp, face, or elsewhere on the body. The most common pattern is a few round or oval bald patches on the scalp, each roughly the size of a coin. The underlying skin remains smooth and unscarred. While psychological stress or illness may trigger the condition in people who are already at risk, most cases have no obvious trigger, and those affected are generally otherwise healthy. In rare instances, all scalp hair is lost (alopecia totalis) or all body hair is lost (alopecia universalis). Hair loss can be either permanent or temporary.
The condition is thought to be an autoimmune disorder, where the body’s immune system mistakenly attacks its own hair follicles during their active growth phase. Normally, hair follicles are protected from the immune system—a state called immune privilege. Alopecia areata occurs when this privilege breaks down, leading to inflammation and halted hair growth. T cell lymphocytes cluster around affected follicles, driving the damage. It is classified as a type 1 inflammatory disease and is not contagious.
Risk factors include a family history of the condition. Among identical twins, if one twin has it, the other has about a 50% chance of being affected. Genetic studies have identified at least four regions in the genome linked to increased risk, and the condition shares genetic risk factors with other autoimmune diseases such as rheumatoid arthritis, type 1 diabetes, and celiac disease—it may even be the only sign of celiac disease. Lifestyle factors like smoking, poor sleep quality, and obesity may also contribute to onset and progression. Smoking is thought to trigger Th17-mediated inflammation in follicles, while sleep disturbances may affect immune function. Obesity is linked to adipokine dysregulation, promoting chronic low-grade inflammation. A defect in endogenous retinoid metabolism is also considered a key part of the disease process. A 2010 genome-wide association study identified 129 single nucleotide polymorphisms associated with alopecia areata, involving genes that control regulatory T cells, cytotoxic T lymphocyte-associated antigen 4, interleukin-2, interleukin-2 receptor A, Eos, and human leukocyte antigen, as well as two genes expressed in hair, PRDX5 and STX17.
No cure exists, but some treatments can speed hair regrowth.
- Field
- Medicine (dermatology)
- Known for
- Autoimmune hair loss condition affecting scalp and body
- Prevalence
- 0.15% of people affected at any one time; 2% affected at some point
- Onset
- Usually in childhood
- Gender ratio
- Females affected at higher rates than males
Lore & Background
Alopecia areata is characterized by small, round or oval bald patches on the scalp or beard, though it can occur on any hair-bearing skin. The underlying skin appears unscarred and normal. Exclamation point hairs—short, narrow near the base—often surround the patches. Hair tends to pull out easily along the edge of a patch. Nails may show pitting or trachyonychia. The disease can go into remission or be permanent, and hair loss and regrowth can occur simultaneously over years.
Reader's Guide
Alopecia areata is a common autoimmune disorder with significant psychosocial impact. It is not contagious. Risk factors include family history, with identical twins having about a 50% concordance rate. Genetic studies have identified multiple associated genes, including those involved in regulatory T cell function and human leukocyte antigen. Lifestyle factors such as smoking, poor sleep, and obesity may contribute. In more than 50% of sudden-onset localized cases, hair regrows within a year; in patients with one or two patches, up to 80% recover within a year. However, many experience multiple episodes. Among those with total body hair loss, fewer than 10% recover. Treatments like triamcinolone injections and 5% minoxidil cream can speed regrowth. Sunscreen, head coverings, and glasses for missing eyelashes are recommended. The condition underscores the complexity of immune privilege and autoimmunity.
Did You Know?
- Alopecia areata is believed to be an autoimmune disease resulting from a breach in the immune privilege of hair follicles.
- Among identical twins, if one is affected, the other has about a 50% chance of also being affected.
- Smoking, sleep quality, and obesity may contribute to the onset and progression of alopecia areata.
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