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Hidradenitis suppurativa (HS), also known as acne inversa, is an inflammatory skin disease that causes painful skin lesions. Affected areas usually include the armpits, inner thighs, groin, genitals, buttocks, and breasts. HS lesions can look like blackheads, pimples, or boils. Lesions usually begin as nodules that can break open, leaking pus. Over time, the skin can scar, and tunnels (called sinus tracts) can form in the skin from repeated HS breakouts.
HS was once thought to be a rare disease, but now it is understood that many people live with HS without being diagnosed. Dermatologists now believe that about 1 out of every 100 people has some form of HS. As hidradenitis suppurativa diagnoses become more common, researchers are learning new information about what causes HS, including its connection to the immune system.
No one knows exactly what causes HS, although doctors now know that it is an inflammatory disease. Doctors used to think the skin condition was caused by blockages in the apocrine sweat glands. They also had the false belief that these blockages were caused by poor hygiene or deodorant and antiperspirant use. It has been thoroughly proven that HS is not caused by poor hygiene and is not contagious.
HS lesions aren’t caused by blockages in the apocrine sweat glands themselves. Instead, HS occurs when hair follicles become blocked and inflamed. HS lesions almost always appear in areas of the body that contain many apocrine sweat glands, but the glands themselves aren’t infected or inflamed — the follicles are to blame for HS symptoms. These areas also tend to be characterized by mechanical friction — areas where skin presses or rubs together. The mechanical friction may also contribute to hair follicle irritation.
Scientists are still unsure what causes these follicles to become so easily blocked and inflamed in the first place. Several factors may play a part in whether you develop hidradenitis suppurativa and how bad the condition gets. Sex hormones might trigger HS, especially for women (who are three times more likely than men to develop the condition). The disease typically manifests after puberty begins, and some women who regulate their hormones with birth control pills may see a decrease in HS symptoms. In addition, some women report that their symptoms improve after menopause.
Environmental risk factors can also affect HS development. Studies have shown that smoking is more common among people who have HS compared to people who don’t have the condition. There is also some evidence that nicotine can trigger inflammatory reactions in the skin for some people. Therefore, doctors recommend quitting smoking to help improve symptoms. Obesity is also more common among people with HS, and some people report that when they lose weight or change their diets, that their HS symptoms improve.
Some studies have looked into whether there may be genetic components to developing HS. To better understand the factors behind this, 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 establishing the genetic basis of HS and translating that genetic evidence into improved treatments or prevention strategies.
Previous genetic studies have found mutations in certain genes that seem to be causing HS in some families, indicating that these genes may affect skin cells, making them more prone to irritation and inflammation. However, Dr. Petukhova believes that there are likely to be many more genes that can 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.
The studies that have been conducted for HS indicate that this will likely be the case for HS as well. For example, about one-third of people with HS report having a family history of the condition, suggesting genetic mutations that cause HS might be passed down through generations for some people.
You may have heard HS described as an autoimmune disease as well as an autoinflammatory condition. Most conditions that involve the immune system are referred to as autoimmune diseases or autoinflammatory disorders. However, while HS inflammation does involve the immune system, researchers don’t know whether HS involves an autoimmune reaction. Currently, HS is only known to be an autoinflammatory condition.
The difference between an autoimmune disease and an autoinflammatory condition is easier to understand once you know that people actually have two types of immune systems — the innate immune system and the adaptive immune system. One produces an autoinflammatory response and the other an autoimmune response. Some immune system conditions produce an autoinflammatory response, some produce an autoimmune response, and some produce both at once. HS may be a condition in which both responses occur at once, but scientists still aren’t sure.
Researchers believe that HS involves an autoinflammatory reaction. Autoinflammatory reactions come from the innate immune system. Innate immune system cells are the body’s first responders. When infectious materials, such as bacteria and viruses, enter the body, these cells rush to the fight. The cells in this category also produce cytokines — chemicals that alert the rest of the body that an invader is present. The ensuing reaction causes the pain and fever associated with inflammation — this is why you develop a fever when you’re ill. However, during an autoinflammatory response, genetic mutations prompt the body to produce these immune cells by mistake — even 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 constantly 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. Just as the innate immune system creates the body’s first responders, the adaptive immune system creates its own special forces — cells called antibodies — which are specially tailored to destroy particular pathogens. The adaptive immune system can essentially remember how to make particular antibodies for some time after an infection ends. This is why you develop immunity to a disease, such as the flu or chicken pox, for a period after you recover.
During an autoimmune reaction, antibodies go rogue. Instead of attacking outside invaders, they attack the body’s own healthy cells, destroying tissue and causing inflammation. Autoimmune reactions might be involved in HS. Scientists have detected elevated levels of certain antibodies in people with HS, but it’s still unclear whether these extra antibodies actually worsen inflammation through an autoimmune reaction. Whether these antibodies are a cause of HS or not, higher antibody levels might be useful predictors of the severity of the disease.
Certain medications can reduce inflammation, preventing new HS nodules and lesions from forming, helping existing HS lesions heal, and generally improving quality of life. These drugs include corticosteroids (usually simply called steroids), which suppress the immune system, reducing the effects of autoinflammatory and autoimmune reactions. However, taking corticosteroids for a long time can lead to other potential side effects, such as high blood sugar levels (leading to diabetes), osteoporosis, high blood pressure, cataracts, and weight gain.
Antibiotics are known to have anti-inflammatory properties also, 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.
For people with severe cases of HS, Humira (Adalimumab) may be an option. Humira is a biologic drug, meaning that it is an antibody designed in a laboratory. During an immune response, your body produces a protein called tumor necrosis factor (TNF), which is one of the causes of inflammation. Humira is a type of antibody called a TNF blocker. It gets rid of the excess TNF to reduce inflammation. Humira is administered through injections. Side effects of Humira can include severe infections.
Humira is the only biologic medication approved by the U.S. Food and Drug Administration (FDA) to treat HS. However, other biologics — Remicade (Infliximab) and Stelara (Ustekinumab) — are sometimes prescribed off-label for HS.
HS is associated with other conditions that stem from problems with the immune system. People who have inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis, are more likely to develop HS, and vice versa. People with HS are also more likely to have 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 of these conditions.
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