"Washing powders cleared of causing rashes," reads the headline in The Daily Telegraph yesterday. The newspaper describes a study that claims the idea that "biological washing powders can trigger skin irritations is a myth with no scientific basis". In the UK in particular, it has been suggested that biological powders and liquid detergents containing enzymes that "digest" dirt and stains, can irritate the skin or aggravate eczema.
The researchers reviewed the scientific literature and looked at the rate of skin reactions following normal or extreme exposure to biological washing powders, particularly those that contain enzymes. They concluded that the potential hazards of enzyme raw materials do not translate into a risk of irritant or allergic skin reactions. Looking at a number of people with skin complaints attributed to laundry products, they "demonstrate convincingly that enzymes were not responsible", the authors add.
Where did the story come from?
Doctor David Basketter and colleagues from St Thomas' Hospital, Nottingham University and St Mary's Hospital carried out this research. The funding for this study was not described, though conflicts of interest and the receipt of consultancy fees from Unilever were declared. It was published in the peer-reviewed British Journal of Dermatology
What kind of scientific study was this?
This was a non-systematic review article. The authors referenced 44 papers that are relevant to the debate about whether enzymes added to detergent washing powders can cause skin reactions. Three skin reactions were looked at: skin irritation, such as hand eczema; allergic reactions that could be detected by blood tests or by testing with patches of the product applied to the skin; or urticaria (hives), a more widespread allergic reaction within minutes of contact.
The researchers do not describe how they searched for relevant scientific literature, but collectively they have extensive experience in managing skin conditions. The article describes the historical background of these "biological" detergents which were first created by adding proteolytic (protein digesting) enzymes to synthetic detergents in the second half of the 20th century. Other enzymes, including amylases (that break down starch) and lipases (that digest fats) have been added more recently.
The authors have described the published studies, the groups of people in whom the experiments were performed and the largely negative findings. Importantly, some of the studies were placebo-controlled and blinded (where the participants were unaware whether they had been exposed to detergents or not) and in some, the biological detergents were compared with ordinary detergents, which can themselves cause irritation. Some studies were in children and some in adults. Some assessed the dangers of occupational exposure to the enzymes in workers who produced the powders.
What were the results of the study?
The main results reported by the researchers are that "enzymes in laundry detergents are not a cause of skin irritation in practice [or] of skin allergy" and that "from first principles, enzymes may have the potential to cause urticaria, but there is no evidence, both occupationally and in consumers, that this actually occurs in practice".
What interpretations did the researchers draw from these results?
The researchers' view is that healthcare professionals should avoid the "mythology" about enzyme-containing laundry products to explain rashes on adults, children or infants. Rather, they should look more carefully for the true cause of eczema in order to come to a correct diagnosis.
What does the NHS Knowledge Service make of this study?
This review article written by experts in the field has described a selected body of research and may well reflect the current state of knowledge in the field. However, some limitations to this type of publication should be considered:
- Non-systematic reviews, those that have not described their searching methods, may fail to detect some publications which could influence the overall conclusion. It is not certain that all studies have shown no effect of these biological powders.
- The quality of the individual studies in the article has not been assessed so the reader is unable to judge how reliable the individual study results are. The ability of researchers to control for hidden bias from the placebo effect or from the unequal selection of participants who took part in these trials would be particularly relevant for an appraisal.
In general, the message from this paper is likely to reflect the opinion of experts in the area and the authors' call for practitioners to carefully look for causes of eczema in order to come to a correct diagnosis, seems like good advice.
Links to the headlines
Washing powders cleared of causing rashes. The Daily Telegraph, May 22 2008
Biological washing powders do NOT cause skin allergies, says expert. Daily Mail, May 22 2008
Bio wash bad myth ,Daily Mirror, May 22 2008