ABSTRACT
Synopsis For patients with skin diseases, the process of treating the skin with topical medications adds to the burden of having the disease. Inconvenient skin reactions can make the treatment troublesome and lower the compliance. Moreover, epidemiological surveys indicate that 50% or more of female consumers believe they have sensitive skin. In the present study, the influence of the vehicle on the adverse skin reaction to lactic acid was judged by the test subjects after application of the test formulations to the facial skin. The results showed a water-in-oil (w/o) emulsion to induce less stinging than an ordinary oil-in-water (o/w) emulsion. Increasing the mineral oil content in the o/w emulsion from 10% to 50% tended (P = 0.077) to decrease the stinging potential of the formulation. An o/w emulsion free from lactic acid but with pH adjusted to 3 using hydrochloric acid induced significantly less stinging than the corresponding lactic acid formulation at pH 3. In conclusion, the present study gives new insights into the influence of vehicle on the stinging capacity of lactic acid, which may be related to its possible penetration via appendages. Hence, encapsulation of the stinging substances in the inner water phase of an emulsion may be a possible option to reduce adverse skin reactions and to increase compliance to water-soluble substances.
