A moisturizer, or emollient, is a cosmetic formulation designed to protect, hydrate, and lubricate the skin. These functions are typically performed by sebum, which is produced by healthy skin. The term “emollient” originates from the Latin verb mollire, which means to soften.
Mechanism of Action In the human body, water continuously evaporates from the deeper layers of the skin through a process called transepidermal water loss (TEWL). The skin’s ability to retain moisture depends on the lipid bilayer between the dead skin cells. Moisturizers work to modify the rate of water loss, with their active ingredients falling into one of two categories: occlusives and humectants.
Occlusives form a hydrophobic coating on the skin’s surface, preventing moisture from escaping. The more occlusive the formulation, the greater the effect. Ointments are more occlusive than aqueous creams, which are more occlusive than lotions. Water loss through the skin is typically around 4-8 g/(m²⋅h). Applying a layer of petrolatum to normal skin can reduce that loss by 50-75% for several hours. Oils naturally produced by the human body moisturize through this same mechanism.
Humectants are Hydrophilic and Absorb Water
They can absorb water from the air and moisturize the skin when the humidity is greater than 70%, but more commonly, they draw water from the dermis into the epidermis, potentially making the skin drier. A study published in Skin Research and Technology in 2001 found no link between humectants and moisturizing effects. In practical applications, they are almost always combined with occlusives.
Moisturizers often contain water, which acts as a temporary hydration agent, facilitating the absorption of some components and evaporation of the moisturizer. They also help smoothen the skin by plugging gaps between dead skin cells.
Types of Moisturizers
There are various types of moisturizers, with petrolatum being one of the most effective, although its oily consistency can be unpopular. Other common moisturizers include cetyl alcohol, Cetearyl alcohol, cocoa butter, isopropyl myristate, isopropyl palmitate, lanolin, liquid paraffin, polyethylene glycols, shea butter, silicone oils, stearic acid, stearyl alcohol, and castor oil, as well as other oils.
Moisturizers may also be available as lotions, creams, ointments, bath oils, or soap substitutes.
Mineral oils and waxes are insensitive to oxidation or rancidity, which has led to their widespread use in emollients and topical medications, replacing vegetable oils.
Moisturizer cosmetics may additionally contain antioxidants, ceramides, emulsifiers, fragrances, penetration enhancers, preservatives, and solvents. Some products are marketed as having anti-wrinkle and skin enhancement effects. Many plant and animal extracts have been claimed to impart skin benefits, with limited scientific evidence.
Applications Moisturizers are used for the treatment of certain skin diseases, such as psoriasis, ichthyosis vulgaris, xerosis, and pruritus in atopic dermatitis. More often, they serve as bases or vehicles for topical medication, such as in Whitfield’s ointment. They are often combined with humectants, such as salicylic acid and urea.
Moisturizers are also widely used in sunscreens, antiperspirants, skin cleansers, shaving creams, aftershaves, and hair tonics.
Moisturizers are used in disposable napkins to prevent dry skin and napkin dermatitis.
Benefits of Moisturizers
A Cochrane review noted that moisturizers show some beneficial effects in eczema. The same review did not find evidence that one moisturizer is better than another. Moisturizers can improve skin comfort and may reduce disease flares in atopic dermatitis. They can be used as leave-on treatments, bath additives, or soap substitutes. There are numerous products available, and the majority of leave-on treatments (from least to most greasy) are lotions, creams, gels, or ointments. None of the different types of moisturizers are more effective than the others, so individuals should choose one or more products that suit their needs based on factors such as age, affected body site, climate/season, and personal preference.
Potential Health Risks of Moisturizers
Over-moisturization: Consistent exposure of the skin to water through moisturization may contribute to an allergic reaction or irritant contact dermatitis and can result in the penetration of foreign objects. Changes in the skin’s normal ecological environment can also support the overgrowth of pathological organisms.
Allergens: Moisturizers containing certain aromas or food additives may trigger an immune reaction or even cause users to develop new allergies. Currently, there is no regulation over the use of the term “hypoallergenic,” and even pediatric skin products with the label may still contain allergens. Those with eczema are especially vulnerable to an allergic reaction to lotions and creams, as their compromised skin barrier allows preservatives to bind with and activate immune cells.
The American Academy of Allergy, Asthma, and Immunology released a warning in 2014 that natural lotions containing ingredients commonly found in food (such as goat’s milk, cow’s milk, coconut milk, or oil) may introduce new allergies and cause an allergic reaction when those foods are later consumed. A paper published in 2021 by researchers at St. George’s, University of London found that frequent skin moisturization in early life might promote the development of food allergies, even when accounting for skin conditions such as eczema.
Fire risk: Paraffin-based skincare products and contaminated clothing can pose a serious fire hazard. Between 2010 and 2018, paraffin was linked to 50 fire incidents (49 of which were fatal) in the U.K. A West Yorkshire Fire and Rescue Service study found that clothing contaminated with cream containing only 21% paraffin, when set alight, was fully engulfed in flame within 3 seconds. The Medicines and Healthcare Products Regulatory Agency (MHRA) released a warning in 2008 about the flammability of paraffin-based products. MHRA recommends that sheets of people using paraffin are changed regularly and that people refrain from smoking or bringing open flames around patients using paraffin. MHRA also recommends that skin creams containing any paraffin have a flammability warning on the packaging.
Popular Moisturizer Brands
- Artistry
- Aveeno
- Bath & Body Works
- CeraVe
- Cetaphil
- Curel
- Dial
- Eucerin
- Gold Bond
- Garnier
- Jergens
- Johnson & Johnson
- Lux
- Neutrogena
- Nivea
- Olay
- Sebamed
- Sensavor
- Simple Skincare
- Suave
- Vaseline
Moisturizers are essential skincare products that serve various purposes, including protecting, hydrating, and lubricating the skin. Understanding their composition, mechanism, and potential health risks can help users make informed choices about which products are best suited for their needs.
