What Is a Humectant?
A humectant is a hygroscopic substance — one that attracts and binds water molecules from its environment. In skincare, humectants are applied topically to draw moisture into the stratum corneum, either from the atmosphere (when humidity is above approximately 70%) or from the deeper dermis. They increase the water content of the outer skin layer, improving hydration, plumping fine lines caused by dehydration, and making skin feel softer and more supple.
Key Humectant Ingredients
Glycerin is the most widely used and well-studied humectant — highly effective at all concentrations from 5–40% and non-sensitising. Hyaluronic acid is a polysaccharide capable of holding up to 1000× its weight in water; different molecular weights penetrate to different skin layers. Sodium PCA is a natural moisturising factor (NMF) component. Urea acts as both humectant and gentle exfoliant. Aloe vera, panthenol (pro-vitamin B5), and honey all contain humectant properties.
The Humidity Problem
In dry environments (below ~40–50% humidity), humectants cannot draw sufficient moisture from the atmosphere and may instead draw moisture from deeper skin layers — potentially increasing transepidermal water loss in very dry conditions. This is why humectants should always be sealed with an occlusive or emollient in dry climates, preventing moisture drawn from the dermis from escaping to the air.
Layering rule: Apply humectant serums to damp (not soaking wet) skin, then immediately follow with a moisturiser containing emollients and/or occlusives to lock in the attracted moisture.
See Humectants Guide and Emollient.