Researchers may have discovered more allergenic ingredients in ordinary shampoos compared with "clean" shampoos.
In a study published in the Journal of the American Academy of Dermatology, researchers evaluated the ingredients of clean shampoos and traditional ingredients in order to establish if there were any differences in the formulations and potential for any allergenic ingredients. In the study, the researchers selected three stores that sell shampoos labeled as "clean." The contents of the shampoo were evaluated for the presence of allergens per the American Contact Dermatitis Society core series, and statistical differences between the two groups were calculated.
The researchers identified a total of 85 clean and 124 traditional shampoos. The use of preservatives was the most significant distinction between the two shampoo categories. Some shampoos labeled as clean were less likely versus traditional shampoos, respectively, to use allergenic chemicals such as methylisothiazolinone (1% vs, 36%, P <.01), methylchloroisothiazolinone (1% vs. 32%, P <.01), and iodopropynyl butylcarbamate (0% vs. 9%, P <.01).
Moreover, the researchers noted, the use of less allergenic preservatives was comparable between clean and traditional shampoos, respectively—sodium benzoate (61% vs. 60%, P = .89), benzyl alcohol (37% vs. 25%, P = .07), and sorbic acid (7% vs. 6%, P = .77). The addition of phenoxyethanol was slightly less common in clean shampoos versus traditional shampoos (41% vs. 56%, respectively, P = .04), and none of the clean shampoos included parabens (0% vs. 9%, respectively).
The authors wrote, "All of the clean shampoos and 99% of traditional shampoos used fragrance. Regarding individual fragrance components, lower rates of cinnamal (9% vs. 34%, P < .01), hexyl cinnamal (8% vs. 34%, P <.01), and cinnamic aldehyde (9% vs. 35%, P <.01) were found in 'clean' shampoos versus traditional shampoos, respectively. In addition, propylene glycol and butylated hydroxytoluene were more common in traditional shampoos versus "clean" shampoos (60% vs. 15%, P <.01) and (15% vs. 1%, P <.01), respectively.” They also noted that “Ultimately ‘clean’ remains an unregulated product disclaimer with various proposed definitions.”
“Based on our findings,” the authors concluded, “‘clean’ shampoos are less likely to use allergenic and controversial preservatives; however, they use fragrance as often as traditional shampoos. Differences in formulation alone cannot predict if 'clean’ shampoos are more or less likely to cause irritant or allergic contact dermatitis in real-world settings.”
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