Indicator washcloth for detecting alkaline washing solutions to prevent dermatitis patients and babies from skin irritation

Introduction The development of smart textiles that yield information on the environment of human beings and their health status is very challenging. The integration of electronics into textiles has reached a high maturity for e.g. heating of napkins, shoe soles, gloves and seats. There have been many approaches to measure heart rate or blood pressure with sensors integrated into textiles (Cherenack and van Pieterson 2012), but none of the textiles have full flexibility, can be washed with a conventional washing machine or can be ironed at temperatures around 200 °C (Stoppa and Chiolerio 2014). These requirements for electronics, and especially their stable encapsulation to withstand humidity and caustic washing agents will probably be overcome in the next years. However, optical sensor technology is fully compatible with textile fabrication processes. Since textile dyes (reactive dyes) with specific indicator functions have become available (Mohr et al. 2008), stable textile sensors can be developed to fulfil all the requirements of the textile industry. Textile indicator dyes can be covalently linked to fibres containing hydroxyl and amino groups, they withstand washing at alkaline pH of conventional washing agents for >50 times, they react fully reversibly and are unaffected by ironing (Lobnik 2012). The objective of the present study is to develop sensor textiles that show a colour change when human skin is exposed to irritating washing agents. This colour change Abstract 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 par‐ ents and elderly people avoid allergic reactions caused by alkaline personal care prod‐ ucts. 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 immobi‐ lised 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.