What is Alopecia Areata?

Alopecia areata is a chronic, immune-mediated disease in which the body's immune system mistakenly attacks the hair follicles, disrupting the normal hair growth cycle and causing hair loss without permanently damaging the follicle itself. It is a common, clinically heterogeneous condition that affects many racial and ethnic groups and does not carry a strong sex predominance.

Onset may occur at any age, but most patients develop the disease before age 40. Early-onset alopecia areata — in pediatric patients under age 10 — tends to represent a more severe subgroup. Hair loss typically begins as one or more round or oval patches on the scalp, though it can also affect the eyebrows, eyelashes, beard, or other body hair. In some cases, small patches merge into larger ones, and in more extensive presentations, hair loss can eventually involve the entire scalp or body. The disease course is unpredictable: hair often regrows on its own, but many patients experience subsequent episodes of hair loss.

Types of Alopecia Areata

Alopecia areata functions as an umbrella term for several clinical presentations, distinguished largely by the extent and pattern of hair loss:

• Patchy Alopecia Areata: The most common form, causing one or more distinct, coin-sized, round or oval patches of hair loss on the scalp or elsewhere on the body. Most cases remain patchy, though the condition can progress to more extensive forms.
• Alopecia Totalis: Results in the loss of all or nearly all scalp hair.
• Alopecia Universalis: The most severe and rarest form, causing complete or near-complete loss of hair on the scalp, face, and body, including eyebrows and eyelashes.
• Diffuse Alopecia Areata: Causes sudden, widespread thinning across the scalp rather than the typical patchy pattern. Because it resembles other forms of hair loss, such as telogen effluvium or pattern hair loss, it can be more difficult to diagnose. 
• Ophiasis: A less common presentation in which hair loss occurs in a band along the sides and back of the scalp. It is generally associated with a less favorable prognosis than other subtypes.

Accurate classification of subtype and extent is important for prognosis and treatment planning, since hair regrowth tends to be more complete in patients with less extensive hair loss, later age of onset, no nail changes, and no family history of the disease.

Risk Factors for Alopecia Areata

A risk factor is any characteristic or exposure that increases the likelihood of developing a disease. While not all individuals with these risk factors will develop alopecia areata, and people without them may still be affected, understanding these factors can inform diagnosis and care.

• Family History: A family history of alopecia areata is present in some patients and is associated with increased risk and a less favorable prognosis for regrowth.
• Genetic Factors: Alopecia areata is considered a multifactorial, polygenic disease. Genome-wide association studies have identified more than a dozen susceptibility loci, most involved in immune regulation. Patients with Down syndrome have a notably increased risk of developing the disease.
• Autoimmune Comorbidities: The disease occurs more frequently in patients with comorbid autoimmune disorders, including thyroid disease, vitiligo, psoriasis, and lupus erythematosus.
• Atopic Disease: Alopecia areata is also associated with a higher rate of atopic conditions, including hay fever, asthma, and eczema.
• Age of Onset: The disease can develop at any age, but most patients are diagnosed before age 40. Earlier onset — particularly in children under 10 — is associated with more extensive, severe disease.

Sources: National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), Cleveland Clinic, National Alopecia Areata Foundation (NAAF), and DermNet