Medically reviewed by Brendan Camp, MD
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- Hidradenitis suppurativa is a chronic inflammatory skin condition that causes deep, painful nodules, which can resemble cystic acne, blackheads, and boils.
- Nodules often turn into abscesses and sinus tracts under the skin, which fill with fluid and are often swollen or firm.
- Over time, many people with untreated HS will develop thick or pitted scarring on or under the skin.
Hidradenitis suppurativa (HS) is a chronic inflammatory skin condition that can easily be confused for acne, so it’s important to know what it looks like so you can treat it correctly. HS occurs where skin frequently rubs against skin, like your armpits, groin, and inner thighs. It typically starts as lumps or boils but often turns into abscesses, which can cause scarring, tunneling, and other skin changes.
Nodules
The first sign of HS is usually a painful, inflamed lump called a nodule under the surface of the skin. Sometimes these nodules look like pimples or ingrown hairs, but they can get larger (up to 2 centimeters across) and last for much longer than a typical blemish. They usually have a circular shape and look redder or darker than the surrounding skin.
Sometimes HS causes blackheads, but these are different from traditional acne-related blackheads. People with HS may have multiple blackheads clustered together or what's known as "double-headed" blackheads, a pair of small, black dots in the same area.
HS nodules can also be mistaken for boils. These infected hair follicles often look the same and appear in similar places, like the armpit and inner thigh, but boils are usually temporary skin infections. HS nodules are chronic, often recurring in the same places, and aren’t caused by bacteria. If you have mild HS, you might only have one or two nodules at a time, but people with moderate or severe HS will typically have multiple nodules at once.
Abscesses
When multiple nodules form in the same area, they tend to cluster together and sometimes even join to create a larger nodule. As this happens, the nodules also fill up with fluid, blood, and pus; this creates what’s called an abscess, or pocket, under the skin. These abscesses are usually swollen or firm and painful to the touch. At some point, they break open, and the fluid inside drains out. This can make a mess on your skin and clothing, and the fluid may have a bad smell.
Tunneling
The more severe or aggressive forms of HS create tunnels called sinus tracts deep under the skin. These tunnels are usually painful and full of fluid and pus that drain out, just like an abscess.
Tunnels often look like uneven ridges or elongated shapes under the skin, and they may have a rough, firm, or rope-like texture. They also usually have at least one opening on the skin’s surface, where the fluid drains from; this might look like a pinpoint or puckered hole or a small open wound. Over time, tunnels can connect to one another and create a larger network underneath the skin.
Scarring
In the later or more severe stages of HS, people may develop scar tissue under or on the surface of their skin. Tunnels left untreated or abscesses that don’t fully heal or recur in the same spots are a common cause of scarring.
You may experience the following types of scars:
- Atrophic scarring: These scars are formed by a loss of skin tissue. They usually look like a depression in the skin, with a sunken or pitted appearance.
- Hypertrophic scarring: These scars are formed by an overgrowth of skin tissue. Hypertrophic scarring is usually thick and fibrous and may look red, pink, or different from your normal skin color. These scars are slightly raised above the surface of the skin. They may flatten over time, but some people’s scars stay raised.
- Keloids: Some people may develop these scars, especially if they are already prone to them. Keloids look a lot like hypertrophic scars and also form from an overgrowth of tissue, but they have a few key differences: They can grow or spread beyond the original injury, may not appear until several months after skin heals, and are less likely to improve over time without treatment. Keloids start out as thickened patches of skin and slowly grow, often changing colors and turning darker than your skin tone. They can be nearly any shape or size but are usually round or elongated. They usually feel firm and rubbery or soft and squishy.
Next Steps
It’s important to recognize the signs of HS as soon as possible: Early treatment makes it easier to manage symptoms, prevent severe complications (like tunneling and scarring), and improve overall quality of life. Many HS treatments also work better when implemented during early or mild stages of the disease.
If you think you have HS, contact a board-certified dermatologist—they are trained to diagnose and treat HS. A dermatologist can prescribe medications to reduce symptoms, help you make a plan to reduce future flares, and also make recommendations for treating late-stage symptoms of HS, like procedures to remove or reduce scarring. If you are struggling with the mental health aspect of having HS, reach out to a mental health provider with experience in chronic illness counseling for additional support.
