There is a preparation of lactic acid or ammonium lactate, which is an alphahydroxy product. When this is applied to the skin, it will cause stinging. These are people that we know have sensitive skin. These people are more likely to get irritated by many different products. Some doctors will actually do a skin test with 10% lactic acid in a cream base and then put it on the skin. 10-15% of the population says that it stings, and the other 80% of the population will not notice anything. It is that 15-20% of the population whose skin is more sensitive, whether it's because they absorb it easier or because of the difference in the stratum corneum, or difference in the moisturization of the skin. My patients who have dry skin will be much more easily irritated by products in the wintertime than they are in the summertime.
