Inverse (flexural) psoriasis: skin folds, symptoms and safe treatment in the UK

Inverse psoriasis is psoriasis in the body folds. NHS inform describes it as affecting the folds or creases in the skin, for example the armpits, groin, between the buttocks and under the breasts, and notes that it can cause large, smooth red patches in some or all of these areas. PCDS lists the axillae, under the breasts, umbilicus, groins, the gluteal cleft, around the anus, the penis and scrotum and the vulva as sites that can be affected.

The word inverse refers to the fact that it affects the flexures, the opposite of the extensor surfaces such as elbows and knees where plaque psoriasis usually occurs. The NHS notes that psoriasis can occur in the folds of the body, such as the groin, genitals and under the breasts, as well as elsewhere.

It can occur alone or alongside plaque psoriasis elsewhere. NHS inform says many people have one type of psoriasis at a time, although two types can occur together and one type may change into another.

PCDS describes flexural lesions as usually symmetrical, very shiny, red and well demarcated. Because of friction and moisture in the folds, the thick silvery scale of plaque psoriasis is often absent, so the skin looks smooth and glossy instead. This is why the condition is sometimes missed or mistaken for something else.

For genital psoriasis, PCDS says the vulva often appears as smooth, non-scaly and red areas, and that scratching can cause infection, dryness and thickening of the skin with further itching. On the penis it often appears as many small red patches on the glans or shaft, which may be scaly or smooth and shiny.

The NHS notes that psoriasis patches may be grey on brown or black skin and can leave dark marks on the skin after the psoriasis has gone.

• Smooth, shiny, well-defined red or darker patches in skin folds.

• Soreness, rawness or itching rather than thick scale.

• Symmetrical distribution, for example both armpits or both groins.

• Worse with sweat, heat and rubbing.

Several conditions look similar in the folds. PCDS gives a specific warning: if affected areas are asymmetrical and scale is present, always consider tinea and send scrapings for mycology. Yeast infection can coexist, which is why PCDS recommends a combined steroid and anti-yeast cream when it is present.

NHS inform says a GP will examine the skin to check for psoriasis and that a biopsy is sometimes needed to find the exact cause, with referral to a dermatologist if the doctor is unsure what is causing the symptoms.

The skin in the folds and on the genitals is thin and absorbs creams easily. PCDS says topical steroids no stronger than Eumovate cream are recommended, that treatment should be stopped once symptoms settle, and that overuse in body folds can cause stretch marks (striae) and long-term aggravation of psoriasis. If a yeast infection is also present, a combination product with an anti-yeast agent should be used.

NICE guideline CG153 agrees: offer a short-term mild or moderate potency corticosteroid once or twice daily for a maximum of 2 weeks for psoriasis of the face, flexures or genitals, and be aware that these sites are particularly vulnerable to steroid atrophy, so steroids should be used only for short-term treatment, 1 to 2 weeks per month. Do not use potent or very potent corticosteroids at these sites.

If the response is unsatisfactory, or continuous treatment is needed and there is a serious risk of local side effects, NICE says to offer a calcineurin inhibitor twice daily for up to 4 weeks, started by a healthcare professional with expertise in psoriasis. PCDS suggests vitamin D compounds or the calcineurin inhibitors pimecrolimus and tacrolimus, noting that both are off-label in psoriasis. NICE also reminds clinicians that topical treatments at these sites may cause irritation.

Emollients are the base of care, and NHS inform lists them as one of the first treatments for mild psoriasis. Systemic and biological treatments are used by specialists when the disease is severe or topical treatment has failed.

NHS inform says friction and sweating make inverse psoriasis worse, so loose clothing, breathable fabrics and keeping the area clean and dry are practical measures, as is addressing weight and triggers. The NHS lists general triggers such as stress, alcohol, smoking, obesity and certain medicines.

Genital involvement can affect intimacy and confidence, and the sources stress that it is worth saying so. PCDS says it is always important to ask, as people may not offer the information themselves, and a GP or dermatologist can help.

On the NHS, a GP can diagnose and treat most flexural psoriasis and will refer to dermatology if the disease is moderate to severe or does not respond, and to a sexual health clinic if genital disease needs a closer look.

Private dermatology or sexual health appointments offer quicker access, and the principles above apply in both settings: mild treatment, short courses and review.