Summary

Hidradenitis suppurativa (HS) is a long-term skin disease affecting young adults, causing multiple boils in skin crease sites such as the armpits and groins. The boils are painful, may produce pus and leave disfiguring scars. How common HS is remains controversial, with recent reports using USA medical insurance data suggesting about 0.1% of the population is affected, which is lower than European studies using self-reported questionnaires (completed by the patient). This may be because insurance databases miss undiagnosed cases. Our study team based in the UK aimed to use UK electronic data recorded by General Practitioners (GPs) to identify known and previously undiagnosed cases of HS. We identified undiagnosed cases by looking for patients who had seen their GP for at least 5 skin boils and validated their diagnosis by sending some of the GPs a questionnaire to double-check. Out of 4.3 million patients in the GP database, we found 23,000 diagnosed HS patients and 10,000 undiagnosed patients, showing that 0.77% of the UK population has HS. Including probable cases, who had 1-4 skin boil consultations, the figure rises to 1.19%. Comparing people with HS to similar people without HS, there are higher rates of smoking and obesity (both 3 times more common), as well as type 2 diabetes, Crohn's disease, raised fat levels in the blood, acne, high blood pressure and depression. However a link was not found between HS and ulcerative colitis or polycystic ovary syndrome. In conclusion, we found that HS is relatively common, nearly 10 times more common than the estimates using USA insurance data. People with HS have higher rates of risk factors for heart disease and stroke and so checking for these conditions is important.