These are the basic building blocks of a cosmetic range, these products are extensively used in the day-to-day cleansing routine and especially when there is change of the outermost layer of the skin barrier and reduced water content in the skin.
Moisturisation traditionally was believed to be done by the occlusion method [using products that inhibited trans-epidermal water loss (TEWL)]. The idea behind this was that the water that originated in the deeper epidermal layers moved upward to hydrate cells in the upper layer of the skin and then, the occlusive ingredient, would be trying to prevent the evaporation loss from happening.
Modern research has now shown that the outer skin acts as a membrane, preforming an active water-barrier function. It has revealed that the skin contains a lot of active water regulating products. These are regulators are often collectively referred to as the Natural Moisturising Factor (NMF). NMF is made up of a mix of low molecular weight soluble hygroscopic substances including lactic acid, pyrollidone-carboxicilic acid and amino acids as well as lipids, lactates, urea, and a number of electrolytes which help preserve water. This naturally collaborative compound mix is thought to be a major player in the membrane process, keeping the horny layer hydrated and flexible.
When the moisture content in the skin is lower than 10%, and there is potentially some damage in the outer skin barrier a person will start to notice that they have a dry skin. To fix this problem re-moisturisation will need to occur.
The moisturiser applied to the skin will need to:
- Repairing the skin barrier
- Increasing water content
- Reducing transepidermal water loss (TEWL)
- Restoring the lipid’s water barrier function
How can this be done
In the table below a number of the most commonly used mechanism are listed:
|Type of action
Physically block TWEL
Attract water to stratum corneum
Smooth Skin by filling spaces between skin flakes, with droplets of oil
|Claims to rejuvenate skin by replenishing essential proteins in skin
Active Ingredient Methodology
The Occlusives are ingredients that physically slow / block trans epidermal water loss (TEWL) in the skin. Petrolatum is recognised as one of the most effective occlusive products followed by lanolin, mineral oil, and silicones such as dimethicone. Petrolatum is widely used as a classic moisturizer and is very effective at a level of 5%. Lanolin is also widely used and quite effective but there is some reluctance in using it due to some external irritation reports. Zinc Oxide is well known and effective extensively used in nappy creams and colours the product white, whilst effective it is limited in its use unless ultra-fine micronized grade is used.
Humectants (latin: humectare = moisten) attracts and retains water when applied to the skin and theoretically improves hydration of the skin. However it should be noted that, the water that is drawn to the skin is trans-epidermal water, not atmospheric water. Uncontrolled continued evaporation from the skin can actually worsen dryness. The operation mode is in that humectants all having Hydroxyl groups. These hydroxyl groups allow them to contribute in the association process known as hydrogen binding. In other words: they attract water. Humectants can be supplied in many forms and includes products such as glycerine, sorbitol, sodium lactate, propylene glycol, MP Diol, Urea, AHA (i.e., lactic acid) and a number of other sugars.
Glycerine: is by far the most popular of all humectants. It is a very effective moisturiser, with good natural connotations but when used at higher concentrations [> 5%] it may sometimes display a sticky, unpleasant feel.
Note that these glycol-type humectant do improve the preservation effect (especially with solubilisation of various parabens) as they help to reduce water from the formulation which many moulds and bacteria require.
Urea & AHA’s (alpha-hydroxy acids): Besides their humectant properties, Urea and AHA’s (e.g. lactic acid) are both keratolytic [designed to dissolve or loosen skin flakes].
Urea is a humectant in lower concentrations (10%), but in higher concentrations (20-30%) it is mildly keratolytic. Urea is structurally the same chemical as is found in the urine of mammals, but the urea we buy and sell is not obtained from urine. It is synthesized from natural gas and chemically pure.
AHA’s, such as lactic acid or glycolic acid, appear to increase cohesion of the stratum corneum (SC) cells, thereby reducing roughness and scaling. Just be very careful with these products as when used in higher concentrations they can have a detrimental, burning, effect on the skin
Emollients and Proteines
Emollients are forms of oil or grease and are thought to fill spaces between skin flakes with droplets of oil, and are not really believed to act as occlusives unless applied heavily. They are providing the skin with a layer of oil to prevent water loss, and lubricating the skin. When emulsified, they help holding oil and water on the skin. Examples are MTC, IPM & IPP, Fatty Alcohols, Fatty acid esters, Cholesterol, Squalane, and structural lipids. Fatty acids and fatty alcohols exercise their benefits through effects on the skin barrier. Examples of these products include stearic, linoleic, linolenic, oleic, and lauric acids, which are found, for example, in Olive oil, coconut oil, and grapeseed oil. Vitamin E is another emollient ingredient commonly used in moisturizers, as are soybean oil and avocado oil. Avocado also contains large amounts of vitamin A and potassium.
These important waxy lipid molecules are found in the cell membrane of skin cells, and are also thought to play a significant role in the water-holding potential of the skin. Ceramide is a major skin cell component and plays a major role in generating multi layered structures. Whilst the natural product is very expensive, synthetic ceramides and oleosomes are now available and have been shown to be very effective in preventing and improving dry skin.
Oleosomes that we have available are emulsifiers that allow you to make cold process or hot process emulsions. These Oleosomes have been clinically proven to enhance the skin barrier, rather than cause irritation like traditional non-ionic emulsifiers
Proteins are claimed to have the great affinity to the skin and are able to leave a film that softens the skin, stretches out some of the fine wrinkles, and avoids water loss. Moisturizers containing collagen and elastin, claim to be able to rejuvenate the skin by replenishing its essential proteins. They provide temporary relief of dry skin by the action of filling irregularities on the skin. Like emollients, when they dry they shrink slightly, leaving a protein film that appears to smooth the skin and stretch out some of the fine wrinkles.
In formulating the ideal moisturizer should be:
- Cosmetically elegant and acceptable
- An effective moisturizer – hydrating the outer skin [reduces and prevents TEWL]
- An emollient – makes skin smooth and supple and reduces TEWL
- An aid in restoring the lipid barrier, i.e., duplicating and enhancing the skin’s natural moisture retention mechanisms
- Moisturizing to sensitive skin – i.e., hypoallergenic, nonsensitizing, fragrance free, non-comedogenic
- Absorbed rapidly providing immediate hydration.
- Long-lasting, affordable
Klein K. Humectants: more than meets the eye (or skin). Cosmetics & Toiletries 2005; 120(2): 30
Lynde CW. Moisturizers: what they are and how they work. Skin Therapy Letters 2001; 6(13): 3
Loden M, Maibach H, Dry Skin and Moisturizers Chemistry and Function. New York:CRC Press 1999.
Harding, C. Bartolone, J. Rawlings A. Effects of Natural Moisturizing Factor. In: Loden M, Maibach H, eds. Dry Skin and Moisturizers; Chemistry and Function. New York: CRC Press 1999.
Tanner F, Beurbe G. Mineral oil and petrolatum – reliable moisturizers. Cosmetic Toiletries 93:81 (1978).
Ghadially R, Halkier-Sorenson L, Elias P. Effects of peterolatum on stratum corneum structure and function. J Am Acad Dermatol 26(3 Pt. 2):387-96 (1992 Mar).