The effect of rheological properties of experimental moisturizing creams/lotions on their efficacy and perceptual attributes

Although anecdotal evidence suggests that the rheology of creams and lotions might affect their moisturizing efficacy and perceptual qualities, to date no systematic investigation of these effects has been carried out. We prepared 12 prototype moisturizing creams that had identical overall formulae but differed in as far as they contained three different polymers (Carbopol 981, Carbopol 5984 and Permulen TR.-2) each at four concentration levels. Using these creams, we carried out two series of experiments. In the first series, we applied pre-determined quantities of creams to defined areas of skin on the forearms of eight panelists and then measured the subsequent changes in Transepidermal Water Loss (TEWL) and Skin Capacitance (SC) values as a function of time. In the second series, the panelists were asked to spread and rub over their entire two hands as much of the creams as they deemed necessary for achieving satisfactory perceived moisturization. In this latter series, we also weighed the amounts of cream used and measured the TEWL and SC values at several skin sites as a function of time subsequent to the cream application. The panelists also scored 14 skin attributes for each of the 12 creams used. The same procedures were also carried out with a commercial skin moisturizing cream (Keri(R)) that was used as a control. In separate laboratory experiments, the rheological properties (i.e. the elastic and viscous moduli) of the various creams at a number of frequencies were measured. The analysis of the experimental results suggested that the overall rheology of creams had little direct effect on both, the moisturizing efficacy and the perceived perceptual attributes. Neither did the overall viscoelasticity or the esthetic attributes of the preparations seem to affect the amounts of creams/lotions that the panelists judged to be necessary for achieving satisfactory perceived hand moisturization. Although all preparations contained the same occlusive material (oil) at identical concentration, nevertheless some of the preparations appeared to show different efficacies depending on the nature and the levels of the polymeric ingredient present.