A new study exploring the epidemiology of alopecia areata was published online in July 2021. In this blog post, we ask Alopecia UK Research Committee member and all-round alopecia areata experts Professor Andrew Messenger and Dr Matt Harries to answer some questions for us and explain what the latest study is all about…

First things first, what is epidemiology and why is it important?

Epidemiology is the study of patterns of disease in a community or a population in order to identify risks or causes, and it can be used to plan and evaluate strategies to prevent illness and to guide treatment. A famous example of an epidemiological study is that by the English doctor, John Snow, who traced the cause of an outbreak of cholera in London to water from the Broad Street pump and curtailed the outbreak by removing the handle from the pump. Examples in more recent times include the identification of smoking as the major cause of lung cancer and looking at risk factors when developing the vaccination strategy in the Covid-19 pandemic.

What epidemiological studies relating to alopecia areata have there been up to now?

Almost all the published studies in alopecia areata that have produced epidemiological information have done so using selected groups of patients, most commonly those attending specialist dermatology departments. But these types of studies do not tell us much about what is happening in the population as a whole – for example, people seeing specialists tend to be more severely affected than those who do not. There has been only one previous study that has looked at alopecia areata across an entire community. This was from Olmsted County in Minnesota in the USA. The results from this study were published in 1995, and updated in 2014 with similar results, giving an idea of the overall frequency of alopecia areata. But the population base was too small to identify whether any particular groups within the population were at increased or reduced risk of developing the disease.

How does this latest study differ from the earlier American study?

Our study included a much larger population base, with over 4 million anonymised GP records being included in the study. This is the largest epidemiology study exploring cases of alopecia areata.

What were the key findings of the study?

Studying the large number of GP records provided the following findings:

Between 2009-2018, 6,675 people in the study population developed alopecia areata for the first time. From this we calculated that about 1 in every 4,000 people develop alopecia areata each year – this equates to about 150 people in a city the size of Sheffield. We call this figure of new cases the incidence of alopecia areata.

At the end of 2018, 1 in 170 people in the study population either had active alopecia areata now or had had it in the past. This figure is known as the prevalence of the disease.

• Alopecia areata was slightly more common in women than in men.
• Alopecia areata can start at any age but the peak age of onset is between 25-29.
• Alopecia areata is more common in people living in urban areas compared to rural areas.
• Alopecia areata is more common in people living in socially deprived areas.
• Alopecia areata is more common in people of non-white ethnicity compared to those of white ethnicity. It was three times as common in people of Asian ethnicity.
• 1 in 4 people with AA are referred to a dermatologist. The proportion increased steadily over the 10 years of the study.

There are some interesting findings here. You have worked with alopecia patients for decades, were any of the findings surprising to you? Were the findings in line with the results of previous studies?

The differences in incidence between the various groups mentioned above did come as a surprise. We were not expecting the urban/rural difference; perhaps the deprivation association was more predictable as it occurs in other diseases but we are unaware of any previous data on this. The main surprise was the ethnic differences, especially the threefold greater incidence in people of Asian ethnicity. There has been a study from the USA reporting alopecia areata as more common in black nurses compared to white nurses so our results are in keeping with this finding. The overall incidence data are very similar to the Olmsted County study from the US – our rate was 0.26 per 1000 patient years, the US figure was 0.21. They found the sex incidence was equal, in ours it was slightly higher in women, but really not much difference.

The study included a very large number of patient records, what are the limitations of the study?

We rely on GPs to make the diagnosis and code correctly. We think the data are pretty accurate but we will undoubtedly have missed some cases that were coded as non-specific alopecia.

We cannot assume that everyone who develops alopecia areata will consult their GP. If they have never had alopecia before, they probably will see their GP but we suspect there are some cases missing. It might also explain why the incidence was slightly lower in men, as research has shown that on average men visit their GP less than women.

In calculating the prevalence of alopecia areata we cannot tell who has current active disease and who has had it previously (and recovered).

We cannot determine the severity of the disease from this study.

There is limited information on treatments. GP prescribing is recorded but not prescribing from secondary care. 

In your summary of the findings, you mention a peak onset of 25-29 years. Does this mean alopecia areata is more common within different age groups?

We can’t tell you how many people have active alopecia areata at any single point in time, nor their age distribution, but we can give you an idea of the incidence of new onset disease by age. The study suggests the incidence rate of alopecia areata per age group to be as follows:

Age 0-4         approx. 1 child in 13,000 per year

Age 4-18       approx. 1 child/teen in 3,500 per year

Age 18-50     approx. 1 person in 2,500 per year

Age 50+       approx. 1 person in 7,500 per year

The question we get asked the most by journalists wanting to do awareness pieces about alopecia areata is ‘How many people in the UK have alopecia areata?’. We have always struggled to answer this, do we now have an answer?

Our results indicate that approximately 400,000 people in the UK either have alopecia areata or have had it in the past. This isn’t the same as the total of the number of people currently affected by alopecia. The National Institute for Health and Care Excellence (NICE) estimate that alopecia areata affects 15 in 10,000 people in the UK. The NICE calculation gives a figure around 100,000 people in the UK currently affected by alopecia. If this means active disease it would seem about right, although we are unsure how this figure was calculated.

How will this latest study help alopecia areata research in the future?

This is ‘hard’ data. It tells us how common alopecia areata is in the population and which groups are most likely to be affected. This information is potentially useful for quantifying health care delivery e.g. in terms of specialist provision, costs of treatments. Over the 10-year course of the study, referral to dermatologists increased from 1 in 5 to nearly 1 in 3 patients diagnosed in primary care – so we need more dermatologists.

The study was sponsored by a large pharmaceutical company which is currently developing new treatments for alopecia areata. Pharmaceutical companies will need data of this type to support the case for drugs being funded by the NHS and other healthcare providers.  If we are to make further progress, we really need continued investment from pharma because, historically, other sources of funding are very limited. So, demonstrating the size of the problem is important.

Finally, the result of the study may give us some clues to causation. For example, the differences across different ethnic groups could possibly relate to pigmentation. There has long been an interest in whether hair pigmentation is relevant to the pathogenesis of alopecia areata. A recent study in white people has found that alopecia areata is more common in those with dark hair. We can only speculate about some of the other findings but you never know when these may become important. 

Thank you to Professor Andrew Messenger and Dr Matt Harries for taking the time to explain this latest alopecia areata study, further details can be found here.

If you have found this blog post interesting, you may also be interested in reading this earlier blog post from Professor Kevin McElwee about the causes of alopecia areata.

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