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Moisturizers

Skin Moisturizers For Acne:

“Dry skin”, or xerosis, is an extremely common problem, and our society, and its advertising suggest that we have a simple solution - just apply a moisturizer. The marketplace has a great number of products to moisturize the skin and dermatologists divide them into different classes, based on how they work.

These classes include:

  • Occlusives
  • Humectants
  • Emollients
  • Protein rejuvenators

What Are Moisturizers?

Moisturizers are bland, oily substances that are applied to the skin by rubbing. They are used to replace natural skin oils to cover tiny fissures in the skin, and to provide a soothing protective film. By doing this, they slow evaporation of the skin’s moisture, thereby improving the appearance and feel of dry and aging skin.

How Do Moisturizers Work?

Traditionally, moisturization was believed to inhibit water loss. Water originates in the deeper skin layers and moves upward to the cells in the stratum corneum, eventually being lost to evaporation. Occlusive moisturization then, prevents the dehydration of the stratum corneum.

Much more is now known about the epidermis, and in particular, the stratum corneum. Dry skin is noted when the moisture content is less than 10%, and there is loss of continuity of the stratum corneum.

Scientifically, the moisturizing treatment involves a 4-step process:

  1. Repairing the skin barrier
  2. Increasing water content
  3. Reducing water loss
  4. Restoring the skin’s ability to attract, hold and redistribute water
Class How does it Work? Example ingredient What is it used for? Possible side effects
I. Occlusive It Physically blocks water loss
  • Petrolatun
  • Lanolin
  • Mineral
  • Oil
  • Zinc Oxide
  • Xerosis
  • Atopic dermatitis
  • Prevention of irritant contact dermatitis
  • Messy
  • Some can cause folliculitis (mineral oil)
  • May cause pimples
  • Some may cause contact dermatitis (lanolin)
II. Humectants Attracts water to the stratum corneum
  • Glycerin
  • Sorbitol
  • Urea
  • Alphahydroxy acids
  • Sugars
  • Xerosis
  • Ichthyosis
  • Skin rejuvenation
  • Some may cause irritation (urea, lactic acid)
III. Emollients Smoothes skin by filling the spaces between skin flakes, with droplets of oil
  • Cholesterol
  • Squalene
  • Fatty Acids
  • Reduces skin roughness
  • They’re not always effective
IV. Rejuvenators They claim rejuvenate the skin by replenishing essential proteins
  • Collagen
  • Keratin
  • Elastin
  • Skin rejuvenation
  • Unlikely to work because the protein molecules are too large to cross the epidermis
  • Some may cause contact dermatitis

Groupings Of Moisturizing Substances Based On How They Work:

Occlusives:

Occlusives are substances that physically block water loss in the stratum corneum. Petrolatum in a minimum concentration of 5% is the most effective occlusive followed by lanolin, mineral oil, and silicones such as dimethicone. Petrolatum is widely used as a classic moisturizer. Lanolin is also widely used and quite effective.

Humectants:

Humectants attract water when applied to the skin and theoretically improve hydration of the stratum corneum. However, the water that is drawn to the skin is water from other cells, not atmospheric water. With this type of moisturizer, evaporation from the skin can continue and actually make the dryness worse. Manufacturers’ attempts to include humectants into moisturizers do not always produce a beneficial effect. High concentrations of propylene glycol and urea can be irritating. Pure mixtures of amino acids are useless as moisturizers. Pure solutions of glycerin are ineffective and propylene glycol by itself is irritating. Alphahydroxyacids, such as lactic acid or glycolic acid, appear to increase cohesion of the stratum corneum cells, thereby reducing roughness and scaling.

Emollients:

Emollients smooth skin by filling spaces between skin flakes with droplets of oil, and are not usually occlusive unless applied heavily. When combined with an emulsifier, they may help hold oil and water in the stratum corneum. Vitamin E is a common additive, which appears to have no effect, except as an emollient. Likewise, other vitamins, for example, A and D, are also added, but their effect is questionable. Examples of emollients include mineral oil, lanolin, fatty acids, cholesterol, squalene, and structural lipids.

Molecules called structural lipids are located between stratum cornea cells, and are also felt to play a considerable role in the water holding potential of the stratum corneum. Ceramide is a major component, natural ceramides themselves are at present too expensive to make commercially available. However, several pseudo-ceramides have been synthesized and clinically shown to be effective in preventing and improving dry skin.

Moisturizers containing collagen and other proteins, that is, keratin and elastin, claim to rejuvenate the skin by replenishing its essential proteins. This is unlikely to occur since these protein molecules are too large to penetrate the skin cells. Protein additives may provide temporary relief from dry skin by filling irregularities in the stratum corneum. 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.

When Are They Used?

  • Dry skin, for example, xerosis, or as a result of metabolic conditions, such as renal insufficiency and/or diabetes
  • Atopic dermatitis
  • Ichthyosis vulgaris
  • Irritant contact dermatitis and prevention6
  • Nummular dermatitis
  • Psoriasis
  • Skin protection, for example, from skin damage due to sun exposure, or to frequent hand washing

Potential Side Effects From Moisturizers:

What Is The Ideal Moisturizer?

The ideal moisturizer should be:

  • An effective moisturizer – providing moisture to the stratum corneum and reducing and preventing water loss
  • An emollient – making skin smooth and supple and reducing water loss
  • An aid in restoring the lipid barrier, that is duplicating and enhancing the skin’s natural moisture retention mechanisms
  • Cosmetically elegant and acceptable
  • Moisturizing to sensitive skin – that is, hypoallergenic, non-sensitizing, fragrance free, non-comedogenic (does not cause pimples)
  • Offered at an affordable price
  • Long lasting
  • Absorbed rapidly providing immediate hydration

Adapted from an article published in the Skin Therapy Letter: Lynde CW. Moisturizers: what they are and how they work. Skin Therapy Lett. 2001 Dec; 6(13):3-5.


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