A specialist in contact dermatitis provided a primer on identifying the most likely causes of allergic rashes in soaps, shampoos, and sunscreens at the 2019 American Academy of Dermatology Annual Meeting which has just ended in Washington
“We are seeing a lot of allergy to personal care products,” Cory A. Dunnick, MD, from the University of Colorado in Denver told Elsevier’s PracticeUpdate.
In personal care products in general, the types of ingredients most likely to cause contact dermatitis are preservatives, surfactants, and perfumes or fragrances.
Patients are more likely to have contact allergic reactions to liquid body washes than bar soaps because liquid body washes are water-based and require a preservative agent and bar soaps do not. So, patients with preservative allergies are safer to choose a bar soap, although they always have the option of scrutinizing ingredients lists to avoid their particular allergen in liquid body washes.
In a study published in Dermatitis last year, Dr. Dunnick and colleagues found that the top preservatives seen in body washes were methylisothiazolinone (MI), quaternium-15, sodium benzoate, a combination of MI and methylchloroisothiazolinone (MCI), DMDM hydantoin, phenoxyethanol, and iodopropynyl butylcarbamate. “All of these are potential allergens,” she said.
An “epidemic” of allergy to isothiazolinones in particular is being observed, said Dr. Dunnick. “In 2005 the US approved MI for use in personal care products and let the concentration to be 100 ppm. The problem is that concentration is too high because MI is a strong sensitizer. Since more products are using MI as a preservative in higher concentrations, more people are being sensitized to that ingredient. In fact, it is the second most frequent allergen the North American Contact Dermatitis Group (NACDG) is seeing positive on patch testing, with rates of 13.4%.”
Every year, the NACDG and the Contact Dermatitis Society (CDS) select an “allergen of the year”. Interestingly, for 2019 they selected parabens as the “non-allergen” of the year. “They wanted to highlight that parabens have an excellent safety record,” explained Dr. Dunnick. “They are used in foods, injectables, topicals, and skin care products. They have a very low rate of sensitization of 0.6% in patch test patients. They are really good preservatives, and they are not very sensitizing.”
With regard to surfactants, one potentially problematic ingredient is cocamidopropyl betaine (CAPB), the “no more tears” ingredient in a popular baby wash. While it is indeed less likely to cause irritation than traditional sodium lauryl sulfate, it is unfortunately more allergenic. The rate of sensitivity to CAPB is 1.6% of patch-tested patients.
Alkyl glucosides are another category of surfactants often implicated in contact dermatitis. “These are very environmentally friendly,” said Dr. Dunnick. “They are made with coconut oil and a starch. There are 19 alkyl glucosides that can be used in personal care products.” Rates of sensitivity to these agents are about 2% patch-tested patients. In addition to soaps and shampoos, these products can be used as emulsion stabilizers or humectants in lotions and sunscreens. They were the NACDG/CDS allergen of the year in 2018.
The final category of products that often cause contact dermatitis are fragrances. “People are adding more botanicals into personal care products and, of course, there are often fragrances in soaps and shampoos,” said Dr. Dunnick. “People mistakenly think that if they are botanical or ‘all natural’ then they are not allergenic.” A related problem is the increasing popularity of essential oils. “You can buy those pure; that’s a 100% concentration, which is going to be more sensitizing. We are seeing allergy to aerosolized essential oils or when people make their own products and add essential oils.
“With patch testing, we are providing personalized medicine; we are giving people personalized recommendations as to what is the best product for them,” concluded Dr. Dunnick. “… We need transparency so that patients can find the right product for them.”
REFERENCE: 2019 American Academy of Dermatology Annual Meeting; https://www.aad.org/meetings/annual-meeting