Products that hydrate the skin play a variety of roles. Hydrators and occlusives
work with the surface of the skin in a barrier function, sup- plying oils and hydration.
Humectants and emollients work within the skin’s layers, attracting and holding
water in the cells, depending on their ability to penetrate.
Hydrators impart a temporary barrier to damaged stratum corneum,
which allows time for reparation of this layer. This enables surface hydration,
treating dry skin that is not necessarily dehydrated. Hydrators of the new millennium
include agents that mimic natural ingredients and functions, stimulating hydration
and repairing the mantle.
Occlusives (also known as lipid barriers) physically block the surface
of the stratum corneum and reduce transepidermal water loss. This increases the
water content in the stratum corneum, producing a state of hydration. Occlusion
is one of the best treatments for dry skin because 1) transepidermal water is the
most effective source of water for the skin, and occlusives prevent excessive water
loss, and 2) these occlusive agents have some emollient effect, as below.
Emollients fill the spaces between the corneocytes, the keratinized
cells of the stratum corneum, providing therapeutic improvement to desquamation
defects. Emollients smooth roughened skin, improve the skin’s appearance, and lubricate
and replace natural skin lipids, providing some occlusion.
Humectants are substances that attract and provide water to the
skin and then bind it to the cells of the epidermis and dermis. The source of the
water for the epidermis is usually transepidermal, from the air and topical products.
The source of hydration for the dermis is derived from the functional aspects of
the layer, such as the blood and dermal production of glycosaminoglycans and other
inherent components, and from topical products designed with sophisticated delivery
systems.