Bathing an infant more than once a week nearly doubles the risk for eczema, and each additional bath increases the risk for skin-barrier dysfunction, according to new research.

"More bathing results in higher transdermal water loss," said investigator Thomas Marrs, PhD, from King's College London.

Maybe we are only meant to bath weekly, he told Medscape Medical News.

Previous studies have looked at bathing frequency in infants with eczema, but this is the first time investigators have looked at bathing in a general population of infants at a time when eczema typically develops, he said.

"Different professionals advise differently. Wash less? Wash more? There's a wide range of difference in awareness of the importance of this," he said. And although this is an observational study, it "tells us there is a relationship between bathing and skin dryness."

Marrs presented results from a recent study on the link between bathing, skin-barrier dysfunction, and eczema at the European Academy of Allergy and Clinical Immunology 2020 Digital Congress.

For their study, he and his colleagues assessed babies from England and Wales who were part of the Enquiring About Tolerance (EAT) study, which evaluated the early introduction of food and allergy development.

Parents completed a questionnaire when their 3-month-old infants were enrolled in EAT, and again at 12 months. They were asked about the use of moisturizer, shampoo, soap, bubble baths, bath oil, and baby wipes, bathing frequency, and their assessment of how dry the baby's skin was.

Infants were assessed at 3 months and 12 months for eczema, using the International Study of Asthma and Allergies in Childhood (ISAAC) protocol, and for transdermal water loss on the left forearm skin.

The risk for eczema at 3 months was significantly higher in babies bathed more than once weekly than in those bathed less often (adjusted odds ratio [aOR], 1.69; P= .03).

"In the first few months of life, there's a pride in routine, in bath, story, bed," Marrs said. However, "I would caution against a daily bathing routine; once a week is enough for a young baby, particularly if they have risk factors for developing eczema."

But for babies who have eczema, bathing should perhaps be done more frequently to avoid infection. For these infants, "this is more complicated," he explained. "Eczema gets more angry when it is left to be infected. The more staph on the skin, the more inflamed. So it may be important to wash more, but we don't know where the balance lies."

At 3 months, skin-barrier dysfunction transdermal water loss of at least 15g/m per h was higher in the 317 infants (24.4%) who had eczema than in the 986 who did not (15.7 vs 12.4g/m per h; P< .001).

And each additional bath per week was independently associated to skin-barrier dysfunction after adjustment for family history of eczema, inherited filaggrin mutation, and family reporting of dry skin and use of emollients (aOR, 1.21; P< .001).

Skin-barrier dysfunction was seen in 14.6% of those bathed no more than once a week, 26.4% in those bathed two to four times a week, 30.4% of those bathed five or six times a week, and 44.0% of those bathed at least daily.

The association between bathing frequency and eczema was lost at 12 months.

"This is really an observational study showing an association in early life," Marrs said. "We need a more robust study. Bathing wasn't absolutely stable from 3 to 12 months of age."

Although less bathing improved transdermal water loss and eczema, it did not improve rates of food sensitization. I

n fact, at 12 months, food sensitization scores were better in frequent bathers.

On skin-prick tests, sensitization was reduced in frequent bathers for peanut (3mm; aOR, 0.22; P= .004) and egg (3mm; aOR, 0.43; P= .04), even after correction for the presence of eczema at 3 months.

"What struck me is that while there was a big decrease in skin sensitization, it wasn't there when we looked in the blood. We can't say there's cause and effect without a clinical trial," Marrs said. "These results were a surprise. It may be that the skin acts as a physical barrier, and if it's dry it's more permeable and more allergens can disrupt skin, which makes it more likely to get sensitization."

The strongest known risk factor of atopic dermatitis is a family history of atopic disease.

"We need to look further at this," he added. Although the study was not powered to look at this, it's "a very good thought teaser."

Around the world, eczema is on the rise, said Umit Sahiner, MD, from Hacettepe University in Ankara, Turkey, during his presentation on causes and current treatment approaches for eczema in children.

"The strongest known risk factor of atopic dermatitis is a family history of atopic disease," he said. "If one or both of the parents have it, the risk for the child is five- or sixfold."

In urban settings, ultraviolet exposure, a dry climate, a diet high in sugars, repeat use of antibiotics, and higher education have all been associated with increased risk for eczema, he said. To date, bathing has not been considered as a risk factor.

Marrs and Sahiner have disclosed no relevant financial relationships.

European Academy of Allergy and Clinical Immunology (EAACI) 2020 Digital Congress.

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Bathing Babies More Than Once a Week Ups Eczema Risk - Medscape