Humectants attract moisture from their environment, which can be the outside air or the underlying layers of your skin. If you are in a humid environment, humectant ingredients will pull in moisture from the air and therefore help your skin to stay hydrated. If you are in a dry climate, on the other hand, humectants can cause your skin to become dehydrated by pulling moisture up from deeper layers and onto the surface, where they can evaporate into the air. For this reason, it is best to combine humectant ingredients with occlusives.
There are many different ingredients that have humectant properties, and some act as both a humectant and an occlusive. Some of the most common humectants are:
Heparan sulfate analog
Alpha hydroxy acids (AHAs)