I. Introduction

Many different factors can contribute to the dysregulated inflammation seen in people with HS. This chapter discusses some of those factors: sex hormones, bacteria living on the skin (the microbiome), body fat, friction, and smoking.

II. Hormones

Sex hormones can play a big part in how severe and painful HS lesions become. Sex hormones, particularly testosterone, can trigger inflammation in both men and women. Many women report bad flares of HS before or during their period. Some women also report their HS improving or worsening during pregnancy, as well as more changes after giving birth. Additionally, some women report that their HS goes away after menopause while others report that the disease remains active.

This tells scientists that the inflammation that causes HS can go up and down when certain sex hormones (like estrogen, progesterone, testosterone) go up and down. However, the challenging part of understanding and studying the relationship between sex hormones and HS is that not everyone is the same. For example, not everyone has changes in their HS disease activity when their hormones change.

III. Bacteria

HS lesions are red, swollen, painful, and leak pus. For many years, people mistakenly thought HS was due to an infection. We now know that the pus from HS lesions is largely sterile, meaning it contains no bacteria.

Yet bacteria still have an important part to play in why the disease occurs. The bacteria on the skin make up what is called the skin microbiome. Some scientists think that the immune system overreacts to normal bacteria (the normal microbiome) on the skin as part of the dysregulated inflammation of HS. Once the inflammation starts, bacteria can form biofilms (thick layers of bacteria that are highly resistant to antibiotics) in HS lesions. In order to properly treat HS, it is important to address biofilms if they are present in the skin; they can be addressed with the use of strong antibiotics or surgery. Aside from their bacteria-killing properties, antibiotics also have anti-inflammatory properties that may be responsible for improving the condition of existing HS lesions and potentially preventing new lesions from forming.

IV. Diet, Weight, and Friction

There is a lot of interest in the area of diet and HS. Some diets help people lose weight, which can help decrease the number of HS flares they have. Some diets contain anti-inflammatory foods, but so far, no specific food has been shown to work in everyone that has HS.

Because fat cells can produce some hormones that make HS worse, losing weight can be helpful by reducing the level of these hormones. Losing weight can also help prevent rubbing and friction that can worsen HS lesions found in skin folds. More information on diet and HS can be found in Chapter 14.

For a long time, it was thought that HS lesions were found in skin folds because of the excessive sweating and rubbing seen in skin folds. Scientists believed that this helped explain why HS predominantly occurred in people who were overweight. We know now that HS can occur anywhere on the body, not just in skin folds, as well as in people of all body weights.

One possible explanation for why HS lesions tend to be found in skin folds is that while friction is not directly causing HS, friction creates an environment that allows HS to develop after certain bacteria and chemicals group together.

V. Smoking

Cigarettes contain many chemicals that can cause inflammation in the body. Scientists think that smoking cigarettes and HS are linked. This is because smoking may trigger inflammation that causes HS and, once the inflammation begins, it is very difficult for it to stop on its own. Scientists are unsure whether vaping is as dangerous as smoking in terms of HS risk factors. Nicotine causes inflammation, but vaping does not contain many of cigarettes’ tar-based chemicals that drive inflammation. Stopping smoking may make your current HS treatment work better.

More research needs to be done on how other forms of smoking, like vaping, influence inflammation in HS. Healthcare providers encourage everyone to stop smoking (even if it is unclear if that will help HS) in order to improve overall health.