We all lose up to a pint of water through our skin’s surface every day. This is called Transepidermal Water Loss (TEWL).

There are factors that increase the rate of transepidermal water loss, including excessive exfoliation, exposure to irritants such as harsh soaps, alcohols, or solvents, and exposure to highly chlorinated water. Environmental conditions also affect the moisture level in our skin: humidity, dry winter air, wind, sun, and pollutants in the air around us all impact our skin.

When the skin’s moisture level is less than 10%, it is considered dry skin.

Moisturizing ingredients work via three different mechanisms: occlusive, emollient, or humectant ingredients.

Occlusives

Occlusives create a barrier over the skin’s surface to stop transepidermal water loss. Examples of occlusives include petroleum jelly, shea butter, mineral oil, or coconut oil. These simple oils and waxes simply sit on the very surface layer of the skin, the stratum corneum, and create a barrier to prevent transepidermal water loss.

Dermalogica Super Rich Repair ($88.00) uses shea butter as an occlusive, and other ingredients add further benefits to this heavyweight cream.

Emollients

Emollients are creams, lotions, or ointments which are able to penetrate beyond the stratum corneum into the deeper layers of the skin. They can help support and bind 

together the proteins that help hold the skin’s cells together, filling in the gaps between the cells and holding water deeper in the skin. Obagi’s KeraPhine Body Smoothing Lotion ($60.00), which contains ammonium lactate, in an emollient-rich lotion for your entire body. Recommended to be applied right after the shower.

Humectants  Humectants work a bit differently – and can be a double-edged sword: Instead of focusing on simply holding water in the skin, these ingredients work by drawing moisture in from the surrounding air. In cases where the humidity is low (like in the winter) they will then draw water molecules up from the deep dermis. If this is not replenished, the skin’s stratum corneum (top layer) may have a shallow level of hydration for the short term but will ultimately become drier than before. Hyaluronic acid is a hard-hitting humectant that can be found in products like Strivectin's Advanced Acid Hyaluronic Dual-Response System ($79.00).

Moisturizers that combine all three types of ingredients are often the most effective. Products like Jan Marini’s Age Intervention Peptide Extreme ($102.00) includes hyaluronic acid and glycerin that act as humectants, collagen as an emollient, and mango seed butter and shea butter that act as occlusives.

It is also incredibly important to remember, just because your best friend likes the particular feel or smell of a particular product, does not mean it will work well for you. When in doubt, always ask the advice of a licensed expert.