Overview
The term ‘moisturizer’ was created by marketers to suggest a cream that increases skin moisture. It is not a scientific definition but is often used interchangeably with the Latin term ’emollient,’ meaning a material designed to soften the skin, even though not all moisturizers are emollients.
Moisturizers are a key part of any skincare routine, especially for individuals who have an altered skin barrier function, increased transepidermal water loss (TEWL), and reduced skin hydration.
It was originally believed that moisturizers worked by preventing transepidermal water loss (TEWL) through occlusion (creating a layer on the skin that traps water inside). However, after the discovery that lipids (particularly ceramides) play a vital role in skin hydration, it is now known that multiple mechanisms are at play. These mechanisms include:
There are three main groups of moisturizers: Emollients, Occlusives, and Humectants.
Occlusives create a barrier on top of the skin to reduce or physically block TEWL and are most effective when applied to wet skin. The most widely used occlusive is petroleum jelly (Vaseline), which can reduce TEWL by more than 98% when used at a minimum concentration of 5%. Other effective occlusive agents include lanolin, mineral oil, and silicones (e.g., dimethicone), which reduce TEWL by 20-30%.
Humectants are hygroscopic, meaning they attract water into the epidermis from the dermis and/or from humid environmental conditions. Since humectants draw water from the dermis, excessive use may exacerbate dry skin conditions. Urea and lactic acid are hydrating humectants at low concentrations; at higher concentrations, they act as chemical exfoliants and increase skin cell turnover. Examples of humectants include urea, hyaluronic acid, and lactic acid.
Why Humectants Alone Are Not Enough
Humectants absorb and retain moisture, much like your skin’s natural natural moisturizing factors (NMF). However, if used alone in a dry environment, humectants can make dry skin worse by drawing moisture from your skin instead of the air. For this reason, humectants should be combined with occlusives, which act as a physical seal to prevent TEWL.
Emollients soften, smooth, and condition the skin by filling in the gaps between cells or skin flakes with droplets of oil. Emollients are mainly oils and lipids. This can help replenish depleted lipids and is effective when ceramides, cholesterols, and fatty acids are combined together. Other popular emollients include aloe vera, shea butter, linoleic acid, oleic acid, stearic acid, and cetyl alcohol. Additionally, some oils, such as mineral oil and jojoba oil, work as both emollients and occlusives.