So-called "natural" creams for eczema have been found to contain the steroid drugs customers were trying to avoid.
Severe eczema cases can be disabling
Researchers from Sheffield tested 24 herbal creams bought from herbalists, clinics and by mail order, and found the majority had traces of the drugs.
Long-term use of steroids for eczema can cause permanent damage.
The results, reported in the journal Archives of Disease in Childhood, have led to renewed calls for tighter regulation of herbal medicines.
Eczema is an increasingly common condition affecting children and adults, and causes itchy rashes, pain and inflammation.
One way of controlling it is by the use of corticosteroid creams prescribed by a doctor.
These can produce a swift improvement, but many people do not want to use them, particularly on children, mainly due the risk of permanent skin damage, growth retardation and hormonal disruption at critical times in a child's development.
Instead, some have turned to herbal medicines, and have paid for creams advertised as "natural" remedies rather than containing steroids.
However, the research, led by Dr Helen Ramsay of the Royal Hallamshire Hospital in Sheffield, suggests that patients may be getting more than they bargained for.
Of the 24 creams they tested, 20 contained "powerful or very powerful" steroid drugs in varying concentrations.
Some - a type labelled "Wau Wa" - appeared simply to be a pharmaceutical steroid brand mixed in a paraffin base.
Instructions suggested that it should be applied "all over", with no mimimum age.
Following these instructions on a four-year-old child would mean applying almost 135 grams of cream a week - exposing children to potentially dangerous levels of steroids.
The cost of the creams varied, but they were often far more expensive than the standard prescription charge.
The findings suggest that little has improved since a similar study in 1999 found eight out of 11 creams tested were similarly laced with steroids.
The practice is illegal, as corticosteroids are a prescription-only medication, and the Medicines and Healthcare Regulatory Agency - formerly the Medicines Control Agency - is vigorous in prosecuting suppliers who distribute such products.
However, Michael McIntyre, a herbalist and the chairman of the European Herbal Practitioners' Association, says that there is a danger of the whole profession being sullied by a few rogue elements.
He has been campaigning for tighter regulation of herbalism in the UK, and is hoping that a new EU directive, alongside UK legislation, could improve matters.
He told BBC News Online: "This is a disaster - people are setting themselves up and there are no controls on them.
"It's an outrageous case - giving out drugs for children that even an adult would not be able to safely put on their face."
He said that he would be surprised if any "herbal" cream would have a swift effect on eczema.
"There are no overnight herbal treatments for eczema - we try to improve things over a longer period.
"The only overnight treatment is a steroid, so if that's what happens after you use a herbal cream, we'd suggest you get it analysed."