Comparison of Contact Allergens in Bar Soaps and Liquid Body Washes
Allergic contact dermatitis (ACD) describes a delayed classic T-cell–mediated (type IV) hypersensitivity immune response to external substances that contact the skin. This often manifests as pruritus, erythema, and vesiculation that may progress to lichenification, xerosis, and fissuring.1 Identification and avoidance of specific allergens are key to adequate management and care.1 Although previous studies have investigated the presence of numerous contact allergens in cleansing products,2 limited research on the contact allergens of specific formulations of cleansing products currently exists. We aim to identify the difference between the number and types of contact allergens found in bar soaps versus liquid body washes.
We examined the top 50 bar soaps and 50 body washes listed on Amazon.com, sorting by “relevance” and filtering by “avg. customer review 4 stars and up” on October 6, 2016. Ingredient lists were almost entirely obtained from Amazon.com, but a few were collected from Target.com, Walgreens.com, and specific product Web sites. Allergens were selected from the American Contact Dermatitis Society core allergen series,3 with the expertise of a coauthor. χ2 and Fisher exact tests were used to compare allergens in bar soaps versus body washes.
Liquid body washes had far more preservative and surfactant allergens compared with bar soaps (P < 0.001, Table 1). No differences in fragrances existed between bar soaps and body washes.
Of the preservatives studied, methylisothiazolinone, quaternium-15, sodium benzoate, methylchloroisothiazolinone/methylisothiazolinone, DMDM hydantoin, phenoxyethanol, and iodopropynyl butylcarbamate were particularly prevalent in body washes compared with bar soaps. Of the surfactants studied, cocamidopropyl betaine and alkyl glucosides were ubiquitous in body washes and rarely seen in bar soaps. Polyethylene glycol was found in 38% of body washes but only in 8% of bar soaps (Table 1).
A number of the most common contact allergens identified by the American Contact Dermatitis Society have been identified in soaps and cleansers3; however, studies investigating these allergens in bar soaps and body washes are limited. Our study revealed a significantly higher number of preservative and surfactant allergens in body washes versus bar soaps.
In recent years, bar soap sales have fallen by 2.2% despite a 2.7% rise in overall bath and shower product sales. Consumers younger than 65 years are primarily responsible. For example, only one third of consumers aged 25 to 34 years are willing to wash their face with bar soap compared with 60% of those older than 65 years.4 Potential explanations for this include the perceived inconvenience of storing bar soaps and the perceived uncleanliness of using them. However, in a study of 16 participants who washed their hands with bar soaps inoculated with gram-negative bacteria, none of the participants had detectable levels of bacterium on their hands after washing.5
Limitations include an inability to specify fragrances in all products because product labels are not required to report specific fragrance compounds. Second, ingredients obtained from retailers such as Amazon.com may be subject to error, although we limited this risk by cross-checking ingredient lists found on other Web sites.
Because ACD often creates a treatment challenge, health care providers will benefit from an improved understanding of potential ingredients in products commonly associated with the condition. The use of bar soaps instead of body washes may alleviate symptoms and improve quality of life in some patients with ACD.