Alopecia areata: what it is and how it differs from common hair loss

When someone starts noticing their hair falling out, the first thing that usually comes to mind is common balding, the inherited kind that creeps up gradually. But not all hair loss is the same. Alopecia areata is a different condition, with its own mechanism and its own warning signs, and it is worth knowing how to recognise them. Here we explain what it is, why it happens according to what we know today, and how it differs from the more usual type of hair loss, without promising anything the evidence does not support.

What alopecia areata is

Alopecia areata is a chronic autoimmune disorder. In simple terms, the immune system itself acts against hair follicles that are in the active growth phase, known as the anagen phase. The most characteristic result is the appearance of bald patches on the scalp. That said, it is not limited to the head: it can also affect the nails, the eyelashes, the eyebrows and other hair-bearing areas of the body.

Behind this process lies what is called loss of the follicle's immune privilege. Normally, the follicle is to some extent protected from the immune response. When that protection breaks down, immune cells such as lymphocytes, dendritic cells and NK cells build up around the root of the follicle, and this triggers a response against its own components.

Why it happens: what we know and what we don't

It is worth being honest: the exact cause of alopecia areata has not been identified. It is considered to be multifactorial in origin, with environmental, autoimmune and genetic factors combining. In fact, there is scientific debate as to whether it is genuinely an autoimmune disease, and no specific autoantigen has been found that is the definitive target of the attack.

What has been described is the role of certain immune messengers and cells. Interferon gamma appears to be a key contributor, and certain cytotoxic T cells have been shown to recognise proteins associated with melanocytes, such as tyrosinase. As for the familial component, some cases have a family history of the condition, which points to an inherited predisposition, even if it does not explain everything.

An important point to dispel a common myth: although stress is often mentioned as a possible trigger or associated factor, it is not established as a cause of alopecia areata. The aetiology remains, to a large extent, unknown.

How it differs from common hair loss

The most frequent type of hair loss is androgenetic alopecia, what we usually call common balding. It is the most common cause in both men and women. To get a sense of its reach, it affects roughly 50% of Caucasian men over 50 and around 50% of Caucasian women over 60, with a somewhat lower prevalence in black and Asian people.

Alopecia areata, by contrast, has an estimated lifetime prevalence of around 2%. And the differences go beyond the figures. Androgenetic alopecia tends to progress gradually, with a more or less predictable pattern, and is closely linked to hormonal and genetic factors. Alopecia areata comes on more abruptly, in well-defined patches, and stems from an autoimmune mechanism. They are distinct conditions, with distinct causes, and that is why they are not managed in the same way. Lumping them together is a common mistake.

• Androgenetic alopecia: the most frequent cause, gradually progressive, linked to hormonal and genetic factors.
• Alopecia areata: autoimmune, with patchy hair loss and a lifetime prevalence of around 2%.
• Both require different approaches; they are not the same disease and are not treated in the same way.

How alopecia areata is diagnosed

Diagnosis is essentially clinical, supported by trichoscopy, a technique that allows a close-up look at the scalp and the follicles. In certain cases a skin biopsy may be needed, although this is not the norm. The examination usually also covers the nails, where changes such as ridging, brittleness or a rough surface may be seen. All of this is assessed by a professional, who is the person able to tell one type of alopecia from another with proper judgement.

What the evidence says about treatment

Here we need to be clear so as not to raise false expectations: as things stand today, there is no treatment that alters the natural course of alopecia areata. There are options that can induce regrowth in severe cases, but that is not the same as a cure.

Specifically, baricitinib and ritlecitinib are authorised by the FDA and by the EMA (and therefore available in Spain through the AEMPS) for patients with severe alopecia areata, and in the United States the FDA also approved deuruxolitinib for adults in 2024. They are inhibitors of what are known as JAK kinases. In studies, baricitinib has shown durable efficacy, with 35 to 40% of patients achieving a significant response (measured with the SALT score) at 36 weeks. The indirect comparison between ritlecitinib and baricitinib has shown similar efficacy, and in ritlecitinib's main trial 23% of patients on the 50 mg dose achieved that response at 24 weeks. It is important to know that long-term treatment is usually needed to maintain regrowth, because stopping is associated with relapse, and that these drugs require monitoring for possible side effects.

One nuance to avoid confusion: the treatments for androgenetic alopecia are different. For common balding there are only two drugs approved by international regulatory bodies, topical minoxidil and finasteride, and they are of no use for alopecia areata. Each type of alopecia has its own approach.

In short

Alopecia areata is an autoimmune disease that causes patchy hair loss and is clearly different from common balding, both in its mechanism and in its treatment. Its exact cause is still not fully understood, and although there are drugs that can encourage regrowth in severe cases, none of them changes the natural course of the disease. If you notice hair loss in specific areas, sudden changes or nail changes, the sensible thing is an individual medical assessment, which is the only way to reach an accurate diagnosis and decide which options make sense in your case.

And if what you are noticing is not patches but the diffuse thinning of common balding, that also has a medical approach today. In Spain that route is medical treatment for hair loss with a prior assessment, a prescription where appropriate from a registered doctor and ongoing follow-up by the medical team. You can check in a few minutes whether you are eligible.