Eczema sufferers may find their condition actually worsening by using an emollient cream meant to treat the irritated skin.
According to tests, a detergent contained in the aqueous cream BP thins the skin and actually causes irritation.
Although aqueous cream has been prescribed for millions of sufferers from childhood, it is the first time research has been carried out on an ingredient called sodium lauryl sulphate (SLS).
Earlier, it was thought the 'stinging' sensation affecting half of users was due to a preservative or antiseptic in the cream.
In a study by Bath University researchers, aqueous cream reduced the thickness of healthy skin in volunteers by more than 10 per cent in just four weeks and water loss was increased.
Professor Richard Guy, professor of pharmaceutical sciences at Bath, said the remedy was likely to aggravate the dry, itchy rashes that plague eczema sufferers.
"The skin has a protective barrier layer of lipids, around one eighth the thickness of a sheet of paper, that stops chemicals from getting into the body and keeps moisture in," the Daily Mail quoted him as saying.
"SLS is a detergent used to mix oils into water-based moisturisation creams to give a nice creamy texture. It's also used widely in shower gels and other cosmetics.
"Our study has found that rubbing aqueous cream containing SLS into the skin thins this protective barrier, making the skin more susceptible to irritation by chemicals. So to use this cream on eczemous skin, which is already thin and vulnerable to irritation, is likely to make the condition even worse," he added.
The study was published in the British Journal of Dermatology.