Occlusive

Occlusives work by sitting on top of the stratum corneum and physically blocking transepidermal water loss (TEWL). Unlike humectants, they do not attract water — they seal it in. Common occlusives include petrolatum, dimethicone, and plant-based waxes. They are most effective when applied to damp skin, layered over humectants so there is moisture to trap. Occlusives are the dominant mechanism behind thick overnight moisturizers and healing ointments.

• Humectant An ingredient that draws water into the skin from the environment or deeper skin layers.
• Emollient An ingredient that softens and smooths skin by filling gaps between skin cells.