Based on a presentation by Diane S. Berson, MD
Watch the video of this Skincare Academy presentation featuring Dr. Berson at https://jcad.tv/sca-diane-berson-update-on-moisturizers/
Dr. Berson is with Weill Cornell Medicine in New York, New York.
What exactly is dry skin?
Basically, dry skin is a lack of water content in the skin. It can be associated with stratum corneum impairment inflammation. It can be influenced by genetics, age, skincare practices, and even the environment, especially the weather. For instance, in the winter, we have cold, dry air outside and steam heat inside; in the summer, most areas normally have very hot, humid weather. When skin is dry, it can be flaky and itchy. When we talk about hydration of the skin, especially the epidermis, we refer to it as a “brick and mortar” model. Essentially, keratinocytes are your bricks and the lipids surrounding the keratinocytes are the mortar.
The stratum corneum lipids are composed of about 50-percent ceramides, 25-percent cholesterol, and 10- to 20-percent free fatty acids. When there is a lack of ceramides, we basically have a defective mortar, and therefore, we have an impaired skin permeability barrier and increased transepidermal water loss.
What is a moisturizer?
A moisturizer is a product that replenishes the mortar—or the intercellular lipids and natural moisturizing factors. It decreases transepidermal water loss and increases skin hydration. It softens the skin, improves flakiness, and helps decrease itch. It also protects the skin from allergens and the environment, and it improves skin barrier function. We know that skin barrier function is compromised in so many of the inflammatory conditions we see in dermatology, including acne, rosacea, eczema, seborrheic dermatitis, and psoriasis.
Types of moisturizers
There are different types of moisturizers: emulsions, which can either be lotions or creams, as well as ointments, gels, and serums.
Emulsions. Emulsions are a mixture of two nonsoluble ingredients, where the internal phase is dispersed in droplets in the external phase. Emulsions can be either oil-in-water or water-in-oil emulsions (Figure 1).
Emulsifiers help keep the two phases together. Emulsifiers include lecithin, polysorbate 60, and cetearyl alcohol. Cationic emulsifiers have emollient properties. While the skin has a net negative charge, these positively charged emulsifiers remain on the skin because of the electrostatic attraction. As previously mentioned, lotions and creams are emulsions, but differ in certain ways. A lotion has a lower viscosity than a cream, and therefore it can be poured. Lotions work well on large body surface areas, such as the arms, legs, abdomen, and the back. Creams, however, have a higher viscosity, cannot be poured, and are typically used for drier skin on the face, elbows, knees, ankles, and hands.
Ointments. Ointments are essentially semisolids comprised of fats, waxes, oils, and hydrocarbons. They have an anhydrous base, which means there is no water in the formula. This also means there are no preservatives, which means less contamination. However, ointments can be aesthetically undesirable for many of our patients who do not like greasy products. However, they are very helpful for incredibly dry, inflamed areas, such as eyelid dermatitis and dry elbows, knees, cuticles, and hands.
Gels. Gels are aqueous-based formulas. They are created using a polymer or other thickening agent, such as xanthan gum, carbomers, or dimethicone cross polymers. They are generally lighter, with a slick consistency, and are great for use on oily skin. Patients who have oily skin and large pores like using gel products because they feel light and nongreasy on the skin.
Moisturizing ingredients
There are different types of ingredients that can comprise a moisturizer. These include occlusives, humectants, and emollients.
Occlusives. Occlusives are oily substances that hold in moisture by reducing water evaporation through occlusion of the stratum corneum. Examples of occlusives include petrolatum, lanolin, mineral oil, vegetable oil, such as soybean oil, dimethicone and cyclomethicone, squalene, waxes, and lanolin. Petrolatum is different from crude oil and is safe for use in cosmetics. A lot of my patients use petrolatum as their last layer to hold in the moisture to the skin. They are essentially repairing the barrier by forming that protective seal, but this practice also can help upregulate antimicrobial peptides, which protect the skin from infection and induce expression of filaggrin and involucrin. Oil-free moisturizers do not contain mineral or vegetable oil, and that’s why we call them oil free. However, they do contain silicone derivative occlusives, such as dimethicone and cyclomethicone. The advantage of silicone derivatives is that they are noncomedogenic, cosmetically elegant, and protective, but less moisturizing than traditional, heavier moisturizers. These oil-free moisturizers also often contain talc, kaolin, starches, and polymer beads. These ingredients, especially talc, are effective at absorbing sebum, minimizing shine, and making pores appear smaller.
Humectants. Humectants attract moisture to the epidermis from the surrounding environment. Humectants can be present in the epidermis and in the dermis. They bind water and hold water in the skin, which helps hydrate the skin. I think our patients have been hearing a lot more about humectants recently, especially hyaluronic acid. The most used humectants in dermatology are hyaluronic acid and glycerin. Other examples of humectants include sorbitol, urea, lactic acid, and filaggrin breakdown products, such as arginine.
Emollients. Emollients provide direct hydration and give partial occlusion. An example of an emollient would be lipids. Emollients fill the spaces between the flaking skin, fulfilling the requirement of the mortar. Emollients include lipids and oils, such as sunflower seed, argan oil, olive, avocado, and coconut oil, rosehip, jojoba, and hemp seed oil. Other examples of emollients include cholesterol, squalene, fatty acids and fatty alcohols, and oatmeal.
Ingredients of special interest
There are a few ingredients of special interest that have become more popular, not only for us in dermatology, but our patients, who are hearing more about these ingredients. These are cosmetically acceptable ingredients that have other properties besides hydrating and moisturizing the skin. These include ceramides, niacinamide, colloidal oatmeal, hyaluronic acid, and hydroxy acids.
Ceramides. Ceramides, again, are part of the mortar in the epidermis of the skin. The most common ceramides in our skin are Ceramides 1, 3, and 6. They have both occlusive and emollient properties and also help restore the skin barrier. Application of ceramides has been shown to increase endogenous ceramide production. We are seeing more ceramides included in moisturizing products and cleansers.
Niacinamide. Niacinamide has become a very popular ingredient in many skincare products. Niacinamide is a form of vitamin B. It has hydration benefits, it increases synthesis of free fatty acids, cholesterol, and ceramides. Niacinamide helps improve barrier function by decreasing transepidermal water loss, but it’s also a potent antioxidant. It also displays potent anti-inflammatory properties through its ability to decrease inflammatory mediators, which worsen the dry sensation in patients with irritated, dry skin. Niacinamide also inhibits the transfer of melanosomes from melanocytes to keratinocytes, making it helpful for fading hyperpigmentation. With all of these benefits, niacinamide has become a very popular ingredient found in moisturizers, anti-aging cosmeceuticals, and products that fade hyperpigmentation.
Colloidal oatmeal. Colloidal oatmeal is very soothing. We use it as a powder in the bathtub when we have rashes, such as poison ivy or chicken pox. Oats contain polysaccharides, proteins, lipids, flavonoids, vitamins B and E, and avenanthramides. Oatmeal has occlusive and emollient properties. Colloidal oatmeal, just like niacinamide, also has antioxidant, anti-inflammatory, and anti-irritant properties. Oatmeal listed in the FDA monograph as a skin protectant that can be labeled for eczema. It can also be considered a prebiotic and is widely accepted as a prebiotic for gut health since it contains nondigestible beta glucans. Recent data suggest that the prebiotic effects on the skin are helpful as well in terms of improving skin hydration, decreasing the skin pH, and increasing microbiome diversity.
Hyaluronic acid. Hyaluronic acid is a glycosaminoglycan. It’s a natural component of the extracellular matrix in the dermis and it’s also present in the epidermis. It modulates inflammation, cellular migration, oxidative stress, wound healing, and again, it’s a very potent humectant. There are various chain lengths of hyaluronic acid. The high molecular weight hyaluronic acid is anti-inflammatory. It’s been shown to decrease interleukin-6 after ultraviolet B-induced inflammation in vitro. Our levels of hyaluronic acid in our skin decrease as we age. Products containing hyaluronic acid allow us to replenish some of that hyaluronic acid to the skin.
Hydroxy acids. Hydroxy acids have the traditional benefit of epidermal exfoliation; that’s why cleansers with alpha hydroxy acids and beta hydroxy acids, such as salicylic acid, are very popular for cleaning the skin. The newer generation hydroxy acids are also effective at hydration, collagen stimulation, and skin barrier repair, with additional antioxidant effects. Products containing salicylic acid and glycolic acid, block glycation and matrix metalloproteinase activity and elastase, which break down collagen. Alpha hydroxy acids such as lactic acid, urea, and glycolic and salicylic acids are humectants.
I hope I’ve given you some valuable information about moisturizing products that we can use to help our patients make their skin feel and look better.