A moisturizer, or emollient, is a cosmetic preparation used for protecting, moisturizing, and lubricating the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

. These functions are normally performed by

sebum A sebaceous gland or oil gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur ...

produced by healthy skin. The word "emollient" is derived from the Latin verb ''mollire'', to soften.

Mechanism of action

In the human body, water constantly evaporates from the deeper layers of the skin through an effect known as transepidermal water loss. By regulating its water content, human skin naturally maintains a dry, easily shed surface as a barrier against pathogens, dirt, or damage, while protecting itself from drying out and becoming brittle and rigid. The ability to retain moisture depends on the lipid bilayer between the dead skin cells. Moisturizers modify the rate of water loss, with active ingredients of moisturizers falling into one of two categories: occlusives and humectants. ''Occlusives'' form a hydrophobic coating on the surface of the skin, keeping moisture from escaping. The more occlusive the formulation, the greater the effect. Ointments are more occlusive than aqueous creams, which are more occlusive than lotion. Water loss through the skin is normally about 4–8 g/(m²⋅h). A layer of petrolatum applied 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 absorb water from humid air (when >70% humidity) to moisturize the skin. More commonly, however, they draw out water from the dermis into the epidermis, making deeper skin dryer. When used in practical applications, humectants are combined with occlusives. Moisturizers commonly contain water, which acts as a temporary hydration agent.

Types

There are many different types of moisturizers. Petrolatum is one of the most effective moisturizers, although it can be unpopular due to its oily consistency. Other popular moisturizers are 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, and other oils. Moisturizers may also be available as lotions, creams, ointments, bath oils, or soap substitutes. Mineral oils and waxes are not prone to

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

or rancidity. For this reason, they have essentially replaced vegetable oils in emollients and topical medication. Moisturizer cosmetics may additionally contain antioxidants,

ceramide Ceramides are a family of waxy lipid molecules. A ceramide is composed of sphingosine and a fatty acid joined by an amide bond. Ceramides are found in high concentrations within the cell membrane of Eukaryote, eukaryotic cells, since they are co ...

emulsifier An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Althou ...

s, fragrances, penetration enhancers,

preservative A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or ...

s, 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, but such claims are presented with little scientific evidence.

Use

Moisturizers are used for the treatment of certain skin diseases, such as psoriasis, ichthyosis vulgaris, xerosis, and pruritus in atopic dermatitis. More often, they are bases or vehicles for

topical medication A topical medication is a medication that is applied to a particular place on or in the body. Most often topical medication means application to body surface area, body surfaces such as the skin or mucous membranes to treat ailments via a large ...

, such as in Whitfield's ointment. They are often combined with humectants, such as salicylic acid and

urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

. Moisturizers are also widely used in sunscreens, antiperspirants, skin cleansers, shaving creams, aftershaves, and hair tonics. Moisturizers are used in disposable diapers to prevent dry skin and diaper dermatitis. Moisturizers show some beneficial effects in treating atopic dermatitis (eczema). Using moisturizers helps to improve skin comfort and may reduce disease flares. They can be used as leave-on treatments, bath additives, or soap substitutes. There are many different moisturizer products, but the majority of leave-on treatments (from least to most greasy) are one of the following: lotions, creams, gels, or ointments. As none of the different types of moisturizers are more effective than the others, people with atopic dermatitis need to choose one or more products according to their age, affected body site, climate/season, and personal preference. However using moisturizers daily in infants during the first year of life does not help to prevent the development of atopic dermatitis, and might even increase the risk of skin infections.

Potential health risks

Over-moisturization

Persistent moisturization to the skin via water contact may contribute to an allergic reaction or contact dermatitis. This could allow foreign objects to penetrate the skin. Changes in the skin's normal ecological environment–either atop or within the skin–can also allow for the overgrowth of pathogens.

Allergens

Aromas or food additives in moisturizers may trigger an immune reaction, including development of an allergy. There is currently no regulation over use of the term "hypoallergenic". In fact, some pediatric skin products marketed as hypoallergenic contained allergens. Those with eczema are especially vulnerable to allergic reaction with 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 lotion containing ingredients commonly found in food (such as goats milk, cow's milk, coconut milk, or oil) may introduce new allergies, potentially causing an allergic reaction upon later consuming such foods. A paper published in 2021 noted that frequent skin moisturization in early life might promote the development of food allergy, even when skin conditions such as eczema are taken into account.

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 in 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 regular paraffin users change their sheets regularly, refrain from smoking and/or bringing open flames near paraffin-coated people or objects. MHRA also recommends that skin creams containing any paraffin have a flammability warning on the packaging.

Brands of moisturizers

* Artistry * Aveeno * Bath & Body Works * CeraVe * Cetaphil * Charlotte Tilbury * Curél * Dial * Diprobase * Eucerin * Gold Bond * Garnier * Jergens * Johnson & Johnson * Lux * Neutrogena * Nivea * Olay * Sebamed * Simple Skincare * Suave * Vaseline

References

{{cosmetics Skin care Emollients and protectives