Inverse psoriasis or HS? How to tell skin fold conditions apart

Key takeaways

• Inverse psoriasis usually forms smooth, shiny patches in skin folds. Hidradenitis suppurativa (HS) often causes deep, painful lumps that return in the same spots.

• Lumps that drain, scar or form tunnels under the skin point toward HS. A dermatologist experienced in HS can confirm it and start treatment.

• A shiny fold rash is more likely inverse psoriasis if you have psoriasis on your scalp, elbows or knees. Tell your dermatologist about psoriasis elsewhere.

• You can have both conditions at the same time. One dermatologist can look at all of your skin and plan treatment around both.

• See a dermatologist if a fold rash or lump keeps coming back. Get care right away for a fever, spreading redness or severe pain.

If you are wondering whether a sore rash in a skin fold is inverse psoriasis or HS (hidradenitis suppurativa), start with its shape. Inverse psoriasis usually shows up as smooth, shiny patches with little scale. HS usually causes deep, painful lumps that return in the same places and can drain, form tunnels under the skin and scar.

On lighter skin, inverse psoriasis patches look red. On darker skin tones, they may look purple, brown or darker than the surrounding skin. The NPF inverse psoriasis overview notes that 21 to 30 percent of people with psoriasis develop this form.

Both conditions favor the armpits, the groin, the skin under the breasts and the area between the buttocks. They can also occur together. A dermatologist can tell them apart and treat either one, or both.

Why skin fold conditions are easy to confuse

A rash in the armpits and groin can come from several conditions. Skin folds trap warmth, moisture and friction, and that changes how a rash looks. Psoriasis in a fold loses the thick scale it usually has on the elbows or knees.

Inverse psoriasis is also called flexural or intertriginous psoriasis, two medical terms for skin folds. Without its usual scale, a smooth patch in a fold can look a lot like irritation or a yeast rash.

HS begins in hair follicles in these same areas. Both are long-term inflammatory conditions that tend to flare, settle for a while and then flare again.

The FDA's HS fact page estimates that HS affects 1% to 4% of people in the U.S., so it is a common condition. Because both favor the same folds, location alone can't tell you which one you have. The look, feel and pattern of your skin give better clues.

Inverse psoriasis or HS, side by side

This table compares the clues dermatologists look for in each condition. Read across each row to see how the two usually differ.

Use these clues to guide your conversation with a dermatologist, who can confirm the diagnosis. One row alone rarely settles the question.

Signs it is more likely HS

Common HS symptoms follow a pattern of deep lumps that keep returning to the same spots. These signs point more toward HS:

• Painful lumps or boils deep in the skin that come back in the same places.

• Lumps that open and drain pus or fluid, sometimes with an odor.

• Tunnels under the skin (sinus tracts) that connect one lump to another.

• Scars where lumps have healed.

• Lumps in the armpits, groin, inner thighs, buttocks or under the breasts.

HS can look like acne, boils or ingrown hairs, so it is often mistaken for them at first. The repeating pattern in the same places is what sets HS apart. Keeping a simple note of where and when each lump appears helps your dermatologist see that pattern.

HS usually starts after puberty, and it can run in families. Our page on hidradenitis suppurativa symptoms and causes explains where HS appears and how it develops.

Signs it is more likely inverse psoriasis

Inverse psoriasis forms flat, smooth patches rather than lumps. These signs point more toward it:

• Shiny patches that look red, purple, brown or darker than the surrounding skin.

• Itching or pain in the fold.

• Patches that get worse with rubbing and sweat.

• Patches under the breasts, between the buttocks or in the genital area.

• Psoriasis elsewhere, such as the scalp, elbows, knees or nails.

• A family history of psoriasis.

Many people with inverse psoriasis also have psoriasis on other parts of the body. Checking your scalp, nails, elbows and knees before your visit gives your dermatologist a useful clue. A family member with psoriasis raises your risk, as our page on psoriasis triggers and treatments explains.

Inverse psoriasis can be mistaken for intertrigo or a fungal rash. If an antifungal cream you've used hasn't helped, tell your dermatologist, because that detail matters.

Can you have both inverse psoriasis and HS?

Yes. Studies find that the two conditions occur together more often than chance would predict.

A 2022 meta-analysis of HS and psoriasis pooled 7 observational studies. It found that people with HS had a 2.67-fold higher risk of having psoriasis. This is an association, and the reason for it isn't fully understood.

Both conditions involve overactive inflammatory signals (immune messengers called TNF, IL-17 and IL-23). They also share risk factors such as smoking and excess weight.

In practice, your dermatologist examines all of your skin to see the whole picture. Treatment can then be chosen with both conditions in mind.

Some biologic medicines treat both conditions. For example, the FDA bimekizumab prescribing information lists moderate to severe plaque psoriasis and moderate to severe HS among its approved uses in adults.

If you already have psoriasis and notice new lumps that drain or return, mention them at your next visit. Your dermatologist can check for HS at the same time.

Other skin fold conditions that can look similar

Several other common conditions also favor skin folds. These clues can help you describe what you see, and a dermatologist can confirm the cause.

• Intertrigo is red, irritated skin on both sides of a fold, caused by rubbing, heat and moisture. The NIH intertrigo overview notes that it often becomes infected, most often with candida.

• A yeast (candida) rash often has small red bumps or pustules, called satellite spots, near the edges.

• Jock itch (tinea cruris) is a fungal infection in the groin, often with a scaly border.

• Folliculitis and boils are infections of hair follicles. They often clear with treatment rather than returning in the same spots the way HS does.

Skin folds are prone to yeast and fungal infections, even when psoriasis is the main problem. A dermatologist can check with a gentle skin scraping and treat both at once if needed.

If your symptoms are mainly under the breasts, our guide to HS under the breasts compares HS with a yeast rash. For the groin, our guide to bumps on your inner thighs covers chafing, folliculitis and jock itch.

How treatment differs

The right diagnosis matters because each condition responds to different treatments. A plan built for one may do little for the other.

Treating inverse psoriasis

Skin in the folds is thin and easily irritated, so dermatologists choose gentler options there. The strongest steroid creams aren't ideal for folds, but many lower-strength steroids suit these areas.

Non-steroid creams are another option. Tacrolimus and pimecrolimus are often used in body folds, and the AAD psoriasis treatment guidance notes that roflumilast cream can effectively treat inverse psoriasis.

Because skin folds are considered a high-impact area, the National Psoriasis Foundation considers everyone with inverse psoriasis a candidate for medicines that work throughout the body. These include biologics (medicines that target specific parts of the immune system). Use prescription creams in folds only as your dermatologist directs.

Treating HS

HS treatment depends on how active the condition is and how much skin it affects. Options can include antibiotics, wound care, pain control, hormone therapies, biologic medicines and in-office procedures for lumps or tunnels that keep returning.

The AAD guide to HS treatment lists three biologics the FDA has approved for moderate-to-severe HS: adalimumab, bimekizumab and secukinumab. Treatment often combines several of these approaches. In-office options can include a steroid injection to calm a painful lump or laser hair removal in affected areas.

Because smoking and excess weight are linked to HS, your dermatologist may also talk with you about quitting smoking and weight management. For a closer look at how antibiotics, biologics and procedures compare, read our guide comparing HS treatment options.

How a dermatologist tells them apart

Specialized training gives dermatologists deep expertise in diagnosing and treating conditions of the skin, hair and nails. That includes rashes and lumps in skin folds that look alike. Deciding whether a fold rash is inverse psoriasis or HS takes a careful look at your history, your skin and sometimes a test.

What happens during the visit

Your dermatologist will ask when the problem started, whether lumps return in the same spots and whether anything has drained. They will also ask about family history and any psoriasis on other parts of your body.

Next, they examine the affected folds along with the rest of your skin, your scalp and your nails. HS is diagnosed mainly from your history and this exam.

If a sore is draining, your dermatologist may swab the fluid to check for infection. A skin scraping can check for yeast or fungus, and a biopsy (a small skin sample examined under a microscope) may be used if the picture is unclear.

You can describe what you've noticed in your own words. For example, you might say, "These sore spots keep coming back under my arms, and one drained last month."

Photograph flares when they happen, since lumps and patches may settle before your appointment. Dated photos show your dermatologist the pattern over time. It also helps to bring a list of creams or medicines you've already tried.

A virtual visit can often start the evaluation with your history, photos and live video. Some cases need an in-person exam, scraping or biopsy, and your care team can coordinate that step. Tono's flagship clinical center in Brooklyn offers in-person care, and patients nationwide are seen virtually.

When to book a visit

Book a visit with a dermatologist if a rash or lump in a skin fold:

• keeps coming back

• hasn't improved with drugstore creams

• drains fluid or pus

• leaves scars

Get care right away if you have a fever, redness or warmth that spreads quickly, or severe pain. Otherwise, seeing a dermatologist early matters. The AAD hidradenitis suppurativa overview notes that treatment from a dermatologist before HS worsens can reduce flare-ups.

Tono's dermatologists treat both psoriasis and HS, so one specialist can work out which condition you have, or whether you have both. Tono offers access to dermatologists within days rather than the traditional months-long wait.

Tono's HS specialty program is our HS Center of Excellence. It covers diagnosis, biologic management, stepping up treatment when needed, long-term care and coordination of procedural care. Tono's co-founder and Chief Medical Officer is Dr. Mondana Ghias, a board-certified dermatologist and recognized authority in HS who has authored more than two dozen peer-reviewed publications, including award-recognized research advancing the treatment of the disease.

Tono has cared for more than 20,000 patients across a 33-state clinical footprint. We accept most insurance, and most plans need no referral, though a few HMOs require one. Our insurance and referral details explain your coverage options.

Frequently asked questions

Is it inverse psoriasis or HS?

Smooth, shiny patches in a fold point toward inverse psoriasis, while deep, painful lumps that keep returning point toward HS. A dermatologist confirms which one it is, or whether it's both.

Why do I have psoriasis in my armpits and groin?

Inverse psoriasis is psoriasis in skin folds, where rubbing and trapped moisture can set off new patches. Psoriasis is driven by the immune system throughout the body, and friction in folds can bring it out in those spots.

Are inverse psoriasis and HS the same condition?

No. Inverse psoriasis is a form of psoriasis, while HS is a separate condition that starts in hair follicles. They can occur together, and a dermatologist can treat both.

Should I try an antifungal or steroid cream first?

It's best to check with a dermatologist first, since the right treatment depends on the cause. Fold skin is thin, and a dermatologist can choose a cream suited to both the cause and the area.

Can a dermatologist diagnose this during a virtual visit?

Often, yes, for the first assessment, using your history, photos and live video. Some cases need an in-person visit to confirm the diagnosis.

Knowing whether you have inverse psoriasis, HS or both is the starting point for a plan that fits your skin. A dermatologist who treats both conditions can sort out which it is and stay with you as your care changes over time. When you're ready, you can schedule an appointment with a Tono Health specialist, in person or virtually.