Consumers and dermatologists alike often believe that with repeated use anti-dandruff treatments become less effective as the body (or the fungus target of many of the treatments) is affected by exposure to the active ingredients.
However, according to scientists at consumer products giant Procter and Gamble (P&G) trials of anti-dandruff products containing pyrithione zinc (the active ingredient in Head and Shoulders) do not show any decline in efficacy over time.
Commonly held belief
The researchers sent out questionnaires to 722 dermatologists based in China, India, Indonesia, the Philippines and the USA in order to get an idea of the prevalence of the belief that efficacy declines over time.
Nearly two thirds of the dermatologists questioned believed that within three months pyrithione zinc products declined in efficiency, according to the study published in the International Journal of Dermatology.
The scientists then tested two products containing pyrithione zinc at 2 percent (with slightly differing base formulations) against the relevant placebos on 248 subjects for 24 weeks.
Subjects were asked to use one of the four shampoos exclusively for 2 weeks and then regularly for the following 22 weeks.
According to the researchers, the results do not show any drop in efficacy of the two pyrithione zinc containing products over the study period.
The team also performed a longer 48 week study, involving 89 subjects and testing both a 2 percent and a 1 percent formula against the relevant placebos.
Within the two study groups, one individual appeared to experience a decreasing deficiency in the treatment and three others were on the borderline, less than 2 percent of the study population.
Chronic problem needs long term solution
The scientists conclude that pyrithione zinc-containing anti-dandruff formulations do not decrease in efficacy over time and that other factors, such as treatment compliance, may explain this commonly experienced problem.
As dandruff is a chronic problem, sufferers are obliged to continue treatment or symptoms may well return, explained the scientists.
An anti-dandruff shampoo, therefore, must perform to the standards a consumer would expect from a non-therapeutic product or they may discontinue use or decrease frequency.
In this respect, qualities such as fragrance and conditioning ability are as important in the treatment products as the normal version.
Price is also important as the consumer will not be willing to pay significantly more for a treatment product if it is to be used on a regular basis, the scientist argued.
Source: International Journal of DermatologyVolume 48, pages 79-85Does tachyphylaxis occur in long-term management of scalp sebhorreic dermatitis with pyrithione zinc-based treatments?James R. Schwartz, Heather Rocchetta, Pravit Asawanonda, Fangyu Luo, Jennifer H. Thomas