Granular parakeratosis: a rash in the skin folds

General information for patients. This page does not replace individual medical advice. Last updated 30 September 2026.

What is it?

Granular parakeratosis, also called hyperkeratotic flexural erythema, is an uncommon rash in the skin folds. It usually affects the groin, armpits, under the breasts or the buttock crease. It looks like red or brown patches with thick, layered, brownish scale, and it can be itchy or sore.

It is not contagious and not dangerous. It can, however, last for months if the cause is not found.

The diagnosis is usually confirmed with a small skin sample (biopsy) or a scraping of the scale examined under the microscope.

What causes it?

The exact cause is not fully understood. Irritation of the skin folds, together with sweat, heat, friction and changes in the normal skin bacteria, all seem to play a part. The most common triggers are products left on the skin:

• Laundry sanitisers and rinse aids containing benzalkonium chloride. This has become a common trigger in Australia. The chemical stays in the fabric after washing and sits against the skin all day.
• Barrier and nappy creams containing zinc oxide.
• Deodorants and antiperspirants (for rashes in the armpits).

Finding your trigger

• Think back to what changed in the weeks or months before the rash started: a new laundry product, cream, deodorant, body wash or wipes.
• Check every laundry product used on your clothes, towels and sheets, including those used by other people in your home or at a laundromat. Words such as “sanitiser”, “antibacterial” or “kills 99.9% of germs” on a laundry product are a clue.
• Read the ingredients for “benzalkonium chloride”, “alkyl dimethyl benzyl ammonium chloride” or “quaternary ammonium compounds”. Some fabric softeners and antibacterial washes may also contain them.
• Look at where the rash is. Rashes where clothing sits tight or gets sweaty (groin, under the breasts, bra line) point to laundry. A rash only in the armpits points to deodorant. A rash in the nappy area points to barrier cream.
• Ask whether anyone else in the home has a similar rash. Shared laundry can affect a whole family.
• Stop all suspect products at once rather than one at a time, so you are not waiting months to test each one.
• Bring the products, or photos of their labels, to your appointment.

The most important step: remove the trigger

Stop the product that may be causing it. Most people improve once the trigger is gone, though it can take weeks to months.

Getting benzalkonium chloride out of clothes

The chemical can stay in fabric through many washes.

• Wash every item that was washed with the sanitiser at least four times in ordinary detergent before wearing it again.
• Clean the washing machine by running an empty cycle, so the residue does not get back into clean clothes.
• Replace what touches the rash if it keeps flaring despite rewashing: underwear, bras, tight leggings, sheets and towels come first. Loose outer clothing matters less.
• Keep laundry sanitisers out of all future washes.

Looking after the skin

• Wash with a gentle soap-free cleanser and pat the skin folds dry.
• Apply a plain moisturiser regularly.
• Wear loose, breathable clothing and try to keep the area cool and dry.

Treatments

Treatment helps settle the rash while the trigger is removed. No treatment has been tested in a clinical trial; the evidence comes from reports of individual patients.

• Creams: a mild steroid cream for a short time, or non-steroid creams such as calcipotriol. Creams that soften scale, such as lactic acid or salicylic acid, may also help.
• Antibiotic tablets: some stubborn cases have cleared with a course of amoxicillin-clavulanate or doxycycline. This suggests skin bacteria may play a part, but results have been mixed.
• Other options: for rashes that persist, other tablets (such as isotretinoin), and occasionally procedures, have been used.
• Anti-fungal creams are mainly useful if there is also a fungal or yeast infection, which can happen in skin folds.

Your dermatologist will choose treatment based on how severe and long-lasting your rash is.

How long does it last?

Once the trigger is removed, the rash usually settles on its own over weeks to months. In one Australian study of 45 people exposed to laundry sanitiser, the rash cleared in everyone with moisturiser, cleaning the washing machine and rewashing or replacing clothes. It can come back if the trigger is used again.

See a doctor sooner if

• The rash becomes very painful, weepy, crusted or has pus (possible infection).
• It spreads quickly or you feel unwell.
• It is not improving within a few months of stopping the suspected product.

Selected references

• Dear K, et al. Hyperkeratotic flexural erythema (more commonly known as granular parakeratosis) with use of laundry sanitizers containing benzalkonium chloride. Clinical and Experimental Dermatology. 2022;47(12):2196-2200. PubMed
• Kumarasinghe SPW, et al. Hyperkeratotic flexural erythema responding to amoxicillin-clavulanic acid therapy: report of four cases. Australasian Journal of Dermatology. 2019;60(4):311-314. PubMed
• Herat A, Gonzalez Matheus G, Kumarasinghe SP. Hyperkeratotic flexural erythema/granular parakeratosis responding to doxycycline. Australasian Journal of Dermatology. 2022;63(3):368-371. PubMed
• Ip KH, Li A. Clinical features, histology, and treatment outcomes of granular parakeratosis: a systematic review. International Journal of Dermatology. 2022;61(8):973-978. PubMed