Rheological Analysis of the Moist Feeling of Lipsticks

“Moist feeling” is one of the most widely used terms to evaluate finishes of lipsticks. However, the relationship between physical properties of lipsticks and this term has not been clear so far. From a result of a users' interview, we have found that the moist feeling can be perceived most strongly when users move their lips immediately after lipsticks were applied. This suggests that the moist feeling is closely related to some dynamic physical properties of lipstick film on a lip. Therefore, we examined mechanical properties of milled lipsticks. Among commercial lipsticks, those evaluated as excellent in moist feeling tend to show a characteristic peak in their tan vs strain profiles. Intensity of this peak can be controlled by modifying wax composition of the lipstick : the score of moist feeling is directly proportional to the peak intensity. These results suggest that this peak can be used as a quantitative index for the improved moist feeling of lipsticks.