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A washcloth with a colour indicator appears green when immersed into skin friendly washing agents with a pH of around 6, and red when immersed into irritant washing solutions with a pH above 9. This traffic light colour change of the washcloth helps parents and elderly people avoid allergic reactions caused by alkaline personal care products. The washcloth operates fully reversibly and thus can be used multiple times, and it can be washed without leaching because the dye chemistry is covalently immobilised to the fabric. Testing according to OekoTex 100 product class 1 approves contact with babies, certifying the high stability of immobilisation. The washcloth can be used for proper choice of skin care products and for general dermatology applications.
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Schaude et al. (2017) studied this question.
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