Hidradenitis suppurativa (HS), also called acne inversa, is an inflammatory skin condition that causes painful skin lesions. These wounds often appear in areas like the armpits, inner thighs, groin, genitals, buttocks, and under the breasts. HS lesions can look like blackheads, pimples, or boils. Lesions usually begin as nodules (small lumps) that can break open, leaking pus. Over time, repeated breakouts can leave scars and tunnels, called sinus tracts.

Although HS was once considered rare, dermatologists now believe it affects more people than previously thought. Around 1 out of every 100 people have some form of HS. As HS diagnosis becomes more common, researchers are learning new information about what causes the condition, including how it might be connected to the immune system.

How Does HS Develop?

No one knows exactly what causes HS, but researchers know that it’s an inflammatory disease. Doctors used to think HS was caused by blocked apocrine sweat glands, which are found in the armpits and groin, and they believed poor hygiene or using deodorant and antiperspirant was to blame. Dermatologists now understand that HS isn’t caused by poor hygiene and isn’t contagious.

HS occurs when hair follicles become blocked and inflamed. HS lesions almost always appear in areas of the body that contain many apocrine glands, but the glands themselves aren’t infected or inflamed — hair follicles cause HS symptoms. HS lesions tend to develop where skin presses or rubs together. This friction may contribute to hair follicle irritation and inflammation.

Sex Hormones

Although scientists aren’t sure why hair follicles become blocked and inflamed in people with HS, several factors may influence how the condition develops and how severe it becomes.

Sex hormones might trigger HS, especially for women, who are three times more likely than men to develop this skin condition, according to a study in Therapeutic Advances in Musculoskeletal Disease.

The same study cites that the condition usually starts after puberty, and some women who regulate their hormones with birth control pills may see a decrease in HS symptoms. Moreover, some women report that their symptoms improve after menopause.

Environmental Factors

Environmental risk factors may also affect HS development. Dermatological studies have shown that smoking is more common among people who have HS compared to people who don’t have the condition. There’s also some evidence that nicotine can sometimes trigger inflammation in the skin. Doctors recommend quitting smoking to help improve symptoms. Obesity is also more common among those with HS, and some people report that when they lose weight or change their diets, their HS symptoms improve.

Genetics

Some studies have looked into the genetic — or hereditary — components of HS. To better understand these factors, myHSteam spoke with Dr. Lynn Petukhova, an epidemiologist and data scientist who studies genetic causes of skin diseases, including HS. Her research program at Columbia University focuses on understanding the genetics of HS to improve treatments and prevention strategies.

Some genetic studies have found mutations (changes, or variants) in certain genes that affect skin cells, making them more prone to irritation and inflammation. However, Dr. Petukhova believes that there are likely to be many more types of genes that influence the onset and progression of HS.

“We know from studying other inflammatory diseases that we can expect to find many more genes, including genes that influence the behavior of skin cells, as well as genes that affect the immune system, for example, making it hyperresponsive to environmental triggers,” she said.

“Larger genetic studies, involving thousands of people with HS, are needed to identify these genes and begin answering some of these questions. The best way for people with HS to find successful treatments ... is to participate in research studies, as well as contribute DNA, so scientists can figure out the connections,” she added.

Researchers haven’t conducted as many genetic studies for HS as they have for some other diseases, such as diabetes, obesity, breast cancer, and others, Dr. Petukhova said. “For those diseases, genetic studies have shown that mutations can sometimes cause disease, or in other cases, just make someone more vulnerable to environmental triggers of disease,” she noted.

Research suggests that genetics may be a key factor in HS. Some studies show that as many as 70 percent of people with HS could have a genetic connection. For example, about one-third of people with HS report a family history of the condition, suggesting that genetic mutations linked to HS may be passed down through families. Additionally, other studies show that around 40 percent of people with HS have a close family member — like a parent, sibling, or child — who is also affected.

Autoimmune or Autoinflammatory?

You may have heard HS described as an autoimmune disease or an autoinflammatory condition. Most conditions involving the immune system are called autoimmune or autoinflammatory disorders. Although HS inflammation does involve the immune system, researchers aren’t sure if it’s caused by an autoimmune reaction. For now, HS is considered an autoinflammatory condition.

The difference between an autoimmune disorder and an autoinflammatory condition is easier to understand once you know that people have two types of immune systems — the innate immune system and the adaptive immune system. The innate immune system is the body’s first defense against infections and injuries. It responds quickly to any threat, causing an autoinflammatory response. The adaptive immune system works more slowly but is more precise. It remembers specific germs or threats and can target them directly. Some immune system disorders produce an autoinflammatory response, some produce an autoimmune response, and some produce both at once. HS may be a condition in which both responses happen at once, but scientists still aren’t sure.

Innate Versus Adaptive Immune System Responses

Researchers currently believe that HS involves an autoinflammatory reaction that comes from the innate immune system, which produces cells that are the body’s first responders. When infectious substances, such as bacteria or viruses, enter the body, these cells rush to the fight and produce cytokines — chemicals that alert the body that an invader is present.

This immune reaction causes the pain and fever associated with inflammation when you’re ill. However, during an autoinflammatory response, genetic mutations prompt the body to produce these immune cells by mistake — when there aren’t bacteria or viruses to fight.

In HS, the autoinflammatory response may be caused by genetic mutations that affect certain skin cells. Because the genes are giving the wrong signals, these skin cells are abnormally inflamed, leading to the symptoms of HS.

Scientists are also studying whether HS involves another type of immune reaction, called an autoimmune reaction. This type of reaction comes from your adaptive immune system. The adaptive immune system creates its own special forces — cells called antibodies — which are tailored to destroy specific pathogens (such as germs or cancer). The adaptive immune system can sometimes learn how to make a particular antibody for some time after an infection ends. That’s why you may develop immunity to a disease, such as the flu or chickenpox, after you recover.

During an autoimmune reaction, antibodies mistakenly attack the body’s own cells instead of harmful invaders, damaging healthy tissue and causing inflammation. Scientists have found higher levels of certain antibodies in people with HS, but it’s still unclear if these antibodies make HS inflammation worse. While it’s not known if these antibodies cause HS, they could help us understand how severe the condition is.

Fighting HS Inflammation

Treatment of HS focuses on reducing inflammation, which can help prevent and heal lesions while improving quality of life. Corticosteroids (steroids) help calm the immune system and reduce its attacks on the body. However, taking corticosteroids for a long time can cause side effects, including high blood sugar (which can lead to diabetes), osteoporosis, high blood pressure, cataracts, and weight gain.

Antibiotics also have anti-inflammatory properties, Dr. Petukhova said. “While antibiotics are often prescribed to help improve HS skin lesions, it remains unclear how much of the effects are due to antibacterial properties of these drugs, and how much is due to the drug reducing inflammation,” she added.

In moderate to severe cases of HS, biologic drugs such as adalimumab (Humira), infliximab (Remicade), or secukinumab (Cosentyx) may be an option. Biologics are human-made antibodies designed in a laboratory and are taken by injection. These drugs work by blocking proteins in the immune system that cause abnormal inflammation. Side effects can include severe infections.

Other Inflammatory Conditions Associated With HS

People with HS have an increased risk of comorbidities (other coinciding conditions) that stem from problems with the immune system. People who have inflammatory bowel disease (IBD), such as Crohn’s disease or ulcerative colitis, are more likely to develop HS.

Likewise, comorbidities of HS include IBD, metabolic syndrome, and inflammatory joint conditions, such as osteoarthritis, rheumatoid arthritis, psoriatic arthritis, and spondylitis. Researchers are exploring whether underlying factors, such as genetics or gut flora, may cause the inflammation associated with all these conditions.

Find Your Team

On myHSteam, the social network for people with hidradenitis suppurativa and their loved ones, more than 44,000 members come together to ask questions, give advice, and share their stories with others who understand life with HS.

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