 White Petrolatum | |
| Type | Cosmetic skincare product |
|---|---|
Amoisturizer, oremollient,[1] is acosmetic preparation used for protecting, moisturizing, and lubricating theskin. These functions are normally performed bysebum produced by healthy skin.[2] The word "emollient" is derived from the Latin verbmollire, to soften.[3]
In the human body, water constantly evaporates from the deeper layers of the skin through an effect known astransepidermal water loss. By regulating its water content, human skin naturally maintains a dry, easily shed surface as abarrier against pathogens, dirt, or damage, while protecting itself from drying out and becoming brittle and rigid. The ability to retain moisture depends on thelipid bilayer between thedead skin cells.[4] Moisturizers modify the rate of water loss, with active ingredients of moisturizers falling into one of two categories: occlusives andhumectants.[5]
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 thanaqueous creams, which are more occlusive thanlotion.[5] Water loss through the skin is normally about 4–8 g/(m2⋅h). A layer ofpetrolatum applied to normal skin can reduce that loss by 50–75% for several hours.[4] Oils naturally produced by the human body moisturize through this same mechanism.[2]
Humectants are hydrophilic and absorb water. They absorb water from humid air (when >70% humidity) to moisturize the skin. Humectants can also draw moisture from deeper layers of the skin to the surface, which may reduce hydration in the lower layers if not combined with occlusives.[6] When used in practical applications, humectants are combined with occlusives.[7] Moisturizers commonly contain water, which acts as a temporary hydration agent.[8]
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.[9][10] Other popular moisturizers arecetyl alcohol,cetearyl alcohol,cocoa butter,isopropyl myristate,isopropyl palmitate,lanolin,liquid paraffin,polyethylene glycols,shea butter,silicone oils,stearic acid,stearyl alcohol andcastor oil, and other oils.
Moisturizers may also be available aslotions,creams,ointments,bath oils, orsoap substitutes. Mineral oils and waxes are not prone tooxidation orrancidity.[11] For this reason, they have essentially replacedvegetable oils in emollients and topical medication.
Moisturizer cosmetics may additionally containantioxidants,ceramides,emulsifiers,fragrances,penetration enhancers,preservatives, andsolvents. 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.
In recent years, manufacturers have increasingly utilized plant-based emollients derived from renewable sources such ascoconut oil,camellia seed oil,avocado oil,rapeseed oil,corn oil,soy oil, andcastor oil.[12] These natural emollients can increaseantioxidant levels in skin and are marketed as gentler alternatives to synthetic compounds. Plant-derived emollient esters exhibit properties such as solvency, pigment wetting, and lubricious substantivity, making them multi-functional ingredients in cosmetic formulations.[13]
Moisturizers are used for the treatment of certain skin diseases, such aspsoriasis,ichthyosis vulgaris,xerosis, andpruritus inatopic dermatitis. More often, they are bases or vehicles fortopical medication, such as inWhitfield's ointment. They are often combined with humectants, such assalicylic acid andurea.[14]
Moisturizers are also widely used insunscreens,antiperspirants,skin cleansers,shaving creams,aftershaves, andhair tonics.[15] Moisturizers are used indisposable diapers to preventdry skin anddiaper dermatitis.
Moisturizers show some beneficial effects in treatingatopic dermatitis (eczema). Using moisturizers helps to improve skin comfort and may reduce disease flares.[16][17] They can be used as leave-on treatments, bath additives, orsoap 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.[18][17] Daily moisturizer use in infants does not prevent eczema,[19][20] and the regular use of moisturizers on healthy infants is not recommended.[21]
Persistent moisturization to the skin via water contact may contribute to an allergic reaction or contactdermatitis.[22] This could allow foreign substances to penetrate the skin, potentially causing allergies or irritation.[23][24] Changes in the skin's normal ecological environment–either atop or within the skin–can also allow for the overgrowth of pathogens, resulting inskin infections.[8] To prevent over-moisturization, moisturizing products should not be applied more than once a day.[21]
Aromas or food additives in moisturizers may trigger an immune reaction, including development of an allergy.[25][26] There is currently no regulation[where?] over use of the term "hypoallergenic". In fact, some pediatric skin products marketed ashypoallergenic containedallergens.[27][28][29] Those witheczema are especially vulnerable to allergic reaction with lotions and creams, as their compromised skin barrier allows preservatives to bind with and activate immune cells.[30] TheAmerican Academy of Allergy, Asthma, and Immunology released a warning in 2014 that natural lotion containing ingredients commonly found in food (such as oats, goats milk, cow's milk, coconut milk, or oil) may introduce new allergies, potentially causing an allergic reaction upon later consuming such foods.[25] Frequent skin moisturization in early life might promote the development of food allergy, even when skin conditions such as eczema are taken into account.[21][26]
Paraffin-based skincare products and contaminated clothing can pose a seriousfire hazard.[31] Between 2010 and 2018, paraffin was linked to 50 fire incidents (49 of which were fatal) in the U.K.[32] 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.[31] TheMedicines and Healthcare products Regulatory Agency (MHRA) released a warning in 2008 about the flammability of paraffin-based products.[33] MHRA recommends that regular paraffin users change their sheets regularly, and refrain from smoking or bringing open flames near paraffin-coated people or objects.[34]MHRA also recommends that skin creams containing any paraffin have a flammability warning on the packaging.[35]
Using emollients from birth does not prevent eczema in infants at high risk...Daily emollient application did not prevent or delay eczema or reduce its severity. There was also no preventative effect on related conditions: food allergy, asthma or hay fever.
