An Overview of Inverse Psoriasis

Inverse psoriasis is an autoimmune condition that causes itchy, smooth lesions in places where your skin rubs together, like the armpits, groin, and under the breasts. It is also known as flexural psoriasis or intertriginous psoriasis.

Inverse psoriasis is rare, accounting for anywhere from 3% to 7% of all psoriasis cases. It disproportionately affects overweight people.

Getting the right treatment can help reduce rashes in skin folds, but inverse psoriasis cannot be cured.

This article reviews the symptoms and causes of inverse psoriasis. It also covers how this condition is diagnosed and treated, and what you can do to better cope with day-to-day discomfort.

Symptoms of Inverse Psoriasis

Inverse psoriasis lesions are:

• Smooth
• Deep red
• Shiny
• Itchy

Because inverse psoriasis affects skin folds, which hold extra moisture, lesions are not dry like skin plaques typical of plaque psoriasis, the more common type.

And because these areas rub together often, skin cells naturally slough off before patches can become scaly.

Pain can accompany inverse psoriasis lesions, particularly where friction is excessive. The delicate nature of tissue within skin folds only increases their vulnerability to injury.

Because of this, it is not uncommon for fissures (cracks) and bleeding to develop.

Warmth and moisture within skin folds also make them a hotbed for bacterial and fungal infections.

Inverse psoriasis can develop exclusively or co-occur with other types of psoriasis, which may come with other signs and symptoms.

Location

Inverse psoriasis appears where skin touches skin, like the armpits. This also differentiates it from plaque psoriasis, which often affects extensor surfaces like the kneecap.

The skin folds most commonly affected are those:

• Around the genitals
• Between in buttocks
• Under the breasts
• In the creases of the groin
• Within the navel
• Behind the ears

In people who are obese, lesions can develop within rolls of abdominal skin, under double chins, between the thighs, and alongside the overhanging skin of the upper arm.

What Causes Inverse Psoriasis?

Inverse psoriasis, like all other forms of psoriasis, is an inflammatory autoimmune disease.

For reasons poorly understood, the immune system will suddenly regard skin cells as harmful and launch an inflammatory assault to control what it presumes to be an infection.

The inflammation causes still-maturing skin cells, called keratinocytes, to develop at an extremely fast rate.

As the cells move from the middle layer of skin (dermis) to the upper layer of skin (epidermis), they start to compress and break through the protective barrier of the epidermis (stratum corneum).

When this happens, the affected skin will thicken and form the lesions recognized as psoriasis.

Inverse psoriasis is not a sexually transmitted disease (STD), though it is sometimes mistaken for one since it can occur around the genitals.

Common Triggers

Little is known about why inverse psoriasis presents in the way that it does. Psoriasis, in general, is believed caused by a combination of genetic factors and environmental triggers.

Among some of the more common triggers of psoriasis are:

• Stress
• Smoking
• Alcohol
• Certain medications, such as beta-blockers and lithium
• Infections, especially strep and upper respiratory tract infections
• Skin trauma, including sunburns, cuts, and abrasion
• Obesity

Others believe that the Koebner phenomenon plays a part. The phenomenon, in which rash develops along the lines of a skin trauma, affects around 25% of people with psoriasis.

The very fact that skin folds rub against each other suggests that the Koebner phenomenon may play a role in aggravating, if not inducing, a psoriatic flare.

Diagnosis

There are no lab tests or imaging studies that can definitively diagnose inverse psoriasis. The diagnosis is primarily based on a visual examination of the skin and a review of your medical history.

In addition to evaluating the lesions, a skin specialist called a dermatologist will look for signs of nail psoriasis and evidence of plaque psoriasis on the scalp or other parts of the body. Many people with inverse psoriasis have one or both of these forms of psoriasis as well, and they often appear first. 

Your medical history may also hold clues, including a family history of psoriasis or risk factors associated with the disease.

If in doubt, a dermatologist may perform a skin biopsy for evaluation under the microscope. Unlike normal tissue, psoriatic tissue will appear hyperplastic (thickened) with acanthotic (compressed) cells.

Considering Other Possibilities

A healthcare provider will also consider all other possible causes to ensure that the appropriate treatment is delivered.

The process, known as a differential diagnosis, will assess for diseases and conditions with symptoms similar to those of inverse psoriasis. These may include:

• Cutaneous candidiasis, a type skin fungus
• Erythrasma, a bacterial skin infection
• Darier's disease (keratosis follicularis)
• Lichen sclerosus, a condition mostly affecting the genitals
• Tinea corporis (ringworm)

Inverse Psoriasis Treatment

Inverse psoriasis cannot be cured, but there are a number of lifestyle changes and medical treatments options to help manage and treat it. Many of these are the same as those used for other forms of psoriasis.

The primary aim of treatment is to bring the skin condition under control by alleviating inflammation, either locally or systemically.

Lifestyle Changes

As a disease closely linked to obesity, inverse psoriasis will almost invariably improve if you lose excess weight.

By eating right and exercising regularly, ideally under the supervision of a body-positive healthcare provider, your overall inflammatory burden can be relieved.

You will also want to take steps to avoid known triggers. This includes, but is not limited to:

• Quitting smoking: No matter how long you have smoked, quitting will render benefits from the moment you put out your last cigarette.
• Cutting back on alcohol: If you drink alcohol, consider stopping or reducing your intake to no more than two to three drinks a day. Avoid non-light beer, which is closely linked to psoriatic flares.
• Reducing stress: Try stress management techniques like deep breathing and meditation to reduce related inflammation.
  

Medical Treatments

Depending on the severity of the symptoms, this may include:

• Topical coal tar preparations
• Topical corticosteroids
• Topical or oral retinoids
• Phototherapy
• Oral disease-modifying antirheumatic drugs (DMARDs) like methotrexate and cyclosporine
• Injectable biologic drugs like Humira (adalimumab), Remicade (infliximab), and Enbrel (etanercept)

With respect to inverse psoriasis specifically, topical antifungals or antibacterials may be used to treat secondary infections that can occur in affected folds of skin. Oral versions may be used in extreme cases. These drugs are not used to prevent disease due to the risk of drug resistance.

In people with inverse psoriasis, the oral antibiotic Aczone (dapsone) appears especially effective. It is typically prescribed in a 100-milligram (mg), once-daily dose until the infection resolves.

Coping

To better cope with the discomfort of inverse psoriasis:

• Wear loose clothing will breathable fabrics.
• Avoid tight belts, collars, and sleeves, as well as leggings and skinny jeans.
• Speak to a healthcare provider about an appropriate fragrance-free antiperspirant. Zinc oxide-based products are often beneficial.
• Apply talcum powder, corn starch, and baking soda to skin folds to keep the skin dry. (Females should avoid using powders in the genital area.)
• Wash your armpits and groin whenever sweaty with cool water and mild soap. Blot (rather than wipe) skin dry.
• Place a thin layer of moisturizer on the affected skin before applying topical medications.
• Take oatmeal baths to soothe inflamed skin.
• Keep your living/work spaces cool to avoid perspiration.

Summary

Inverse psoriasis is a type of psoriasis that appears in body parts where the skin rubs together. This might include the armpits, groin, or folds of skin on the abdomen. Lesions are red, smooth, shiny, and itchy.

The condition is most common in people who are obese and can be triggered by stress, infections, and skin trauma.

Your healthcare provider may recommend topical creams, injectable medication, or lifestyle changes to help manage the condition.