What Is Alopecia Areata?

Alopecia is the medical term for hair loss. Although hair loss can run in families (for example, male and female pattern baldness), some types of hair loss have other causes. The term “alopecia areata” specifically describes hair loss that is caused by an autoimmune condition.

What Causes Alopecia Areata?

Autoimmune conditions are caused by the immune system mistakenly recognizing the body’s own tissue as foreign and attacking it. This results in inflammation (the process by which your body responds to an injury or a perceived threat, such as a bacterial infection). Although it is not fully understood how or why, alopecia areata involves the immune system mistakenly attacking hair follicles, which stops them from growing hair. Because alopecia areata does not cause scarring to the scalp, the hair may begin to regrow over time, but it is not guaranteed and there is a risk of more hair loss in the future.

Alopecia areata can occur at any age and causes sudden hair loss that can develop anywhere, often in the form of small, round, coin-sized bald patches. Some people experience a burning, itching, or tingling sensation in the skin underneath the hair before it is lost. Compared with the rest of the population, people with alopecia areata are slightly more likely to develop or have another autoimmune condition, such as type 1 diabetes and vitiligo. There also appears to be a link with allergic conditions such as asthma and eczema.

What Did This Study Investigate?

Although alopecia areata is known to be an autoimmune condition, the causes of the immune system starting to attack the hair follicles are not well understood. There are no known links with a poor diet or vitamin deficiencies, and although there is some evidence that stress can trigger alopecia areata, many people with the condition do not report significant stress so this may be coincidental. However, the development of the condition can be very upsetting, particularly if a person is unable to disguise their hair loss with their hairstyle, and some studies have reported that alopecia areata is associated with an increased risk of someone having anxiety and/or depression. The authors conducted a nested case–control study to look for evidence of associations of alopecia areata with lifestyle factors and disorders that affect people’s mental health.

What Is a Nested Case–Control Study?

Different types of studies can be used to investigate factors that cause conditions. A nested case–control study is a type of observational study. These are so-called because the people conducting the study observe what happens to a group of people over time without any manipulation or intervention. “Prospective” observational studies involve researchers following a group of people (cohort) over a long period of time, watching out for outcomes and then looking for patterns that suggest factors that may contribute to or prevent them.

In contrast, “retrospective” observational studies look backwards from an outcome and review information about the participants’ pasts to try to identify associations. Case–control studies are usually retrospective. They compare a group of people with the condition that is being investigated (cases) with a second, similar group of people that do not have it (controls). If a case–control is “nested”, several healthy control participants are selected for each case.

What Did the Study Show?

The authors used information collected by the All of Us research program, a diverse health information database that anyone in the USA can join, to analyze the health data of 957 adults with a diagnosis of alopecia areata matched 1:4 (1 case to 4 controls) with 3,828 controls by age, sex at birth, and self-reported ethnicity. The results showed that when compared with controls, people with alopecia areata were more likely to have depression and anxiety. There were also associations with post-traumatic stress disorder, obesity, and increased alcohol use, although people with alopecia areata were less likely to smoke.

The authors suggest that the association with post-traumatic stress disorder supports the idea that stress plays a role in the dysregulation of the immune system that leads to alopecia areata. They also note that the increased likelihood of obesity in people with alopecia areata may be related to the effects of mental health conditions, which may result in people being less physically active. The increased alcohol use may similarly be influenced by people having mental health disorders, in addition to the distress that some people experience when alopecia areata develops.

On the basis of these results, the authors suggest that people with alopecia areata should be referred to patient support groups by their dermatologist. They also recommend that patients are screened for anxiety, depression, post-traumatic stress disorder, alcohol use disorder and other health issues, with referral to specialist health care practitioners as necessary.