If you have hidradenitis suppurativa (HS), you may develop tunnels underneath your skin. These hollow connections typically form between infected HS bumps. If left untreated, the tunnels, also called sinus tracts, can form permanent scar tissue that limits your mobility.

In this article, we’ll discuss what HS tunnels are, why they form, and how your health care provider treats them. It’s important to work closely with your dermatologist (skin specialist) to prevent tunnel formation and improve your quality of life with HS.

Formation of Tunnels in Hidradenitis Suppurativa

HS is an inflammatory skin condition that causes lumps or nodules to form underneath the skin. These nodules can look like acne, pimples, blackheads, or cysts (fluid-filled bumps). Sometimes, the lumps go away on their own.

Over time, HS nodules can grow and join together. They eventually form abscesses — or painful nodules filled with blood or pus. They can also burst and leak fluid.

If left untreated, hollow tunnels can connect abscesses underneath the skin. The American Academy of Dermatology notes that tunnels form when abscesses repeatedly heal and reopen.

Research shows that having multiple HS tunnels is associated with:

• More severe disease activity
• Less response to medications, like biologics
• Severe pain
• Reduced quality of life

Symptoms of Hidradenitis Suppurativa Tunnels

You might relate to this member’s experience: “Does anyone get a bump or tunnel that never heals, it just refills with fluid? It’s not really painful, but it’s irritating because it leaks when it wants without warning.”

HS tunnels can fill with fluid, pus, or blood. If a tunnel connects to the surface of your skin, it may leak and give off an odor. Tunnels can also create scar tissue and leave behind permanent scars. Scar tissue isn’t as flexible as healthy skin. Thick scars can become severe enough that they limit your range of motion (how far you can move a body part).

Where Do HS Tunnels Develop?

In HS, your immune system mistakenly attacks your hair follicles. This produces inflammation that leads to nodules and abscesses. Tunnels can develop anywhere you have these lumps.

HS tends to affect certain areas of skin, especially where you have more hair follicles or your skin rubs together. Places where HS tunnels may form include the:

• Armpits
• Breasts or area below
• Waist or lower part of the abdomen
• Inner thighs
• Groin area
• Genitals
• Buttocks
• Area of skin between the genitals and anus

Tunnels can also cover large areas of skin and connect multiple lumps. One member shared, “I’m afraid that my tunnels are now spreading from just below my butt to my inner thighs. I’ve been dressing them, but the sores on my inner thighs are oozing a lot.”

Research shows that HS tunnels can form in the three layers of skin. These layers have different functions:

• Epidermis — Top layer, which makes new skin cells
• Dermis — Middle layer, which contains hair follicles, blood vessels, and nerves
• Hypodermis — Bottom layer, which contains connective tissue to cushion bones and muscles

Treatments for Hidradenitis Suppurativa Tunnels

Doctors use a combination of surgery and medications to treat HS tunnels. A few types of surgery can be used for HS and tunnels. Your dermatologist or surgeon will choose a procedure depending on the location of your tunnels and how severe your symptoms are.

One myHSteam member shared their experience with surgery. “Just had surgery under my arm to remove the sinus tract last week,” they said. “That was the last bump from HS. I’ve been doing so good — no breakouts at all.”

Doctors can also use medications to treat inflammation and reduce the number of nodules and abscesses you have. This can help limit tunnel formation.

Deroofing

Deroofing is typically used in the first two stages of HS. During this procedure, the surgeon removes the “roof,” or skin on top of the tunnel, and scrapes out the tissue inside the tunnel. The healthy cells from the hair follicles and sweat glands then heal the wound.

A myHSteam member described their experience with deroofing surgery: “My surgeries consisted of slicing open the top of the nodule, scraping out the infection and tunnels, and laying skin back over the wound.” Studies show that deroofing is generally successful and prevents HS lesions from returning.

Incision and Drainage

To relieve HS symptoms, doctors may suggest incision and drainage. The doctor numbs the affected area and makes a small cut (incision) in the abscess, then drains fluid or pus from the area.

The relief from incision and drainage is usually temporary. Your abscesses will probably return, so this procedure is less favored.

Wide Excision

If your HS tunnels can’t be treated with other surgeries or medications, your dermatologist may recommend wide excision. This procedure removes the entire tunnel along with fat or skin around it. Your surgeon may use imaging tests to determine the tunnels’ location and size.

Surgeons usually leave a wide excision wound open to heal on its own. In some cases, you may need another surgery to replace the removed tissue. Your surgeon can use some of your own healthy skin to make a skin graft to cover the wound. This helps it heal properly.

Biologics

Doctors also use medications known as biologics to treat HS. Biologics are lab-engineered protein drugs that help dampen inflammation.

The U.S. Food and Drug Administration (FDA) has approved two biologics to treat moderate to severe HS — adalimumab (Humira) in 2015 and secukinumab (Cosentyx) in 2023. Studies show that adalimumab and secukinumab help reduce the number of nodules, abscesses, and tunnels from HS. A third biologic, bimekizumab (Bimzelx), showed promising results in phase 3 clinical trials and is seeking FDA approval. This drug was approved for psoriasis, another skin condition, in 2023.

Infliximab (Remicade) isn’t FDA-approved for HS, but some doctors prescribe it off-label (outside its approved use). Research has found that infliximab also helps keep nodules, abscesses, and draining tunnels from forming.

Researchers are also studying new biologics in large studies or clinical trials for treating HS. One example is brodalumab, which targets inflammatory chemical messengers known as interleukins. A team of scientists from New York University found that brodalumab treatment may help reduce drainage from tunnels. While these results suggest potential benefit, more research is needed on brodalumab for HS.

Prevention of Hidradenitis Suppurativa Tunnels

The best way to prevent tunnels is to manage your HS symptoms. Your health care provider or dermatologist may prescribe these medications to treat HS:

• Antibiotics, such as dapsone or clindamycin
• Oral retinoids, such as isotretinoin
• Hormonal medications, such as spironolactone (Aldactone) or birth control pills

By following your treatment plan, you can help stop nodules and abscesses from forming and leading to HS tunnels.

Talk With Others Who Understand

On myHSteam, the social network for people with hidradenitis suppurativa, more than 39,000 members come together to ask questions, give advice, and share their stories with others who understand life with HS.

Do you have tunnels with your hidradenitis suppurativa? What symptoms have you experienced? What treatments have you used? Share your experience in the comments below, or start a conversation by posting on your Activities page.