Measuring the frequency of consumer hair combing and magnitude of combing forces on individual hairs in a tress and the implications for product evaluation and claims substantiation.

Abstract

It is commonly assumed that, due to the long growth cycle of hair, multi-cycle combing, and strength and fatigue testing using thousands of cycles is relevant for product evaluation and claim substantiation. The objective was to assess the frequency and magnitude of combing forces on individual hairs against a hypothesis that fibres on a consumer's head rarely experience significant loads during routine combing. Single fibres were removed from a tress, attached to a load cell and replaced in the tress. Combing of tresses, guided by in-vivo measurements, measured the frequency of significant loads defined as 'events' ≥1 g over 30 combing sets (set = 10 comb strokes @~25 cm s-1 ) with intermediate tangling. Asian and Caucasian hair was assessed by dry, wet, bleached-wet and bleached-dry combing. A questionnaire of 231 Asian and Caucasian women established daily frequency and number of comb strokes for the whole head. In-vivo combing videos of 10 women (five Asian, five Caucasian) were used to establish in-vivo and tress combing speeds. The questionnaires returned an average combing frequency of 1.7×/day (range 0-5) and average number of strokes 16 ± 2.3 per head/day (95% CI). Video analysis measured combing speeds of 22-35 cm s-1 across hair types. Tress data confirmed individual fibres are unlikely to experience repeated loading or significant loads in all but wet combed persulphate bleached hair. 'Events' of ≥1 g - dry combing gave an event probability of 0.2 and average load of 1.7 g over 30 comb sets. Dry combed bleached samples returned a probability of 0.23 and 0.3 respectively. Wet combed virgin Asian and Caucasian hair gave a probability of 0.1 and 0.47 respectively. Wet combed bleached hair gave a probability of one. The addition of a conditioner to bleached hair reduced the event probability to <0.1. During combing, individual fibres may not experience any significant loads and are unlikely to experience repetitive loads >10 g. The low number of comb strokes and low event probability is in keeping with consumers growing their hair long and in good condition. The data indicates the need for a significant rethink of methods used for product evaluation and claim substantiation.