Clinicians should consider potentially harmful ingredients such as haptens when using moisturizing emollients to prevent atopic dermatitis or food allergy, according to a review published in Clinical and Translational Allergy.
This careful selection is especially important when treating young children, Klaudia Ryczaj, MD, of the department of pediatric pneumonology and allergy at Medical University of Warsaw in Poland, and colleagues wrote.
The review included 12 clinical trials published through December 2020 involving a total of 16 different emollient preparations that were applied as interventions. Each trial examined one to five emollients used to enhance the skin barrier; researchers found that each trial had at least one emollient that included a contact allergen, or hapten.
Also, 12 of these 16 preparations (75%) included at least one hapten — a small molecule that elicits an immune response only when it is attached to a large carrier such as a protein — from the common patch test series. Most of these haptens were emollients, preservatives and emulsifiers.
According to the researchers, more than half of the contact allergens that were identified also had potential as irritants. For example, propylene glycol, which the researchers called a well-known skin irritant, was identified in two emollients used in three of the trials.
The researchers also noted that lanolin displays considerable risk for development of allergic contact dermatitis. Neither lanolin nor propylene glycol are recommended for use in children aged younger than 2 years, but they were included in products used in four (33%) of the trials.
Six of the trials included cosmetics with phenoxyethanol, which is a preservative that has low sensitizing properties, according to the researchers. Its widespread use in cosmetics, however, has led to similar sensitization rates to lanolin.
Isopropyl myristate, which the researchers also identified as a hapten in the trials, increases skin permeation by fitting into the lipid lamellae and changes the microstructure of the stratum corneum. It is used as a penetration enhancer in topical and transdermal formulations.
The researchers noted that the risk for allergic sensitization to emollients in preventive AD therapy cannot be predicted due to the unknown concentrations of multiple contact allergens in these cosmetics.
The researchers also cautioned that not all moisturizers improve the function of skin barriers and that some may even impair skin barrier function. These moisturizers damage the stratum corneum, remove skin lipids, increase susceptibility to irritants and accelerate transepidermal water loss.
Additionally, the prolonged use of emollients in preventive therapy for AD could lead to increased risks for skin infections as well as for AD and food allergy by altering the microbiome, according to the researchers.
The researchers emphasized that 75% of the emollients studied in these trials included at least one common contact sensitizer. Ceridal Lipogel, paraffin-based bath oils, liquid paraffin and pure sunflower seed oil were the only products in the trials that did not include any common haptens.
Calling allergic contact dermatitis one of the most common pediatric skin disorders and noting that it may even begin early in infancy, the researchers called for further research to validate their suppositions as well as careful selection of emollients when treating younger children.