Our skin is the largest organ of the human body and carries out very important functions. It protects us from small injuries and from sun radiation, plays a role in temperature control and water loss, and is the first line of defense against germs.
Being constantly on the frontline, our skin is exposed to a number of factors that may cause damage. Dry skin is a common condition that can affect our appearance as well as cause other unpleasant symptoms.
Treatment choices for dry skin usually fall between self-remedies and therapeutic products. In this review, we will focus on moisturizers, and in particular their ingredients and functions.
What is dry skin?
The composition of our skin is more complex than it may seem on the surface. The epidermis is the outermost layer, followed by the dermis and the more internal subcutaneous. The epidermis also has several layers, with the stratum corneum, also known as the skin barrier, being the external one. The main components of the stratum corneum are dead cells and fat molecules.
Among the fat molecules, ceramides are very important because they function as a barrier that protects the skin and maintains hydration. Damaged skin is not as effective in preventing water loss by evaporation.
Dry skin can be rough to the touch, scaly and very itchy, while cracking of the skin may happen in the most severe cases. Areas of the body that are more likely to develop dry skin are the thighs, lower legs, arms and the sides of the abdomen.
What causes dry skin?
The causes of dry skin are numerous. Some are environmental and include overexposure to the sun and low humidity. Low humidity can be a consequence of climate, electric heat, fireplaces and air conditioning. Other possible factors might be related to medical conditions such as diabetes and liver disease, but also normal aging and genetic predisposition.
Habits such as bathing in hot water too frequently, swimming in chlorinated pools and using harsh perfumed deodorants or antibacterial soaps can also lead to dry skin. Before starting treatment, a medical evaluation can help distinguish dry skin from other conditions such as atopic dermatitis, psoriasis and fungal infection.
The original purpose of moisturizers was to deliver fat molecules back to the skin after cleansing. Over time, they have become a vehicle for delivering a variety of substances to our skin. Nowadays, moisturizers aim to make skin soft, improve its hydration and appearance, and deliver other ingredients.
There is a myriad of different moisturizers commercially available; they come in different formulations based on their specific application and can contain a great variety of ingredients. Despite the variety, the majority of moisturizers contain similar basic ingredients. Below, we will discuss the most dermatologically relevant ingredients of moisturizers.
Top five moisturizer ingredients for dry skin
Occlusives are substances that form an impermeable barrier, which prevents water loss and promotes skin repair. This is the most effective and most common moisturizing method. The cosmetic industry can choose from a great assortment of occlusive agents.
Petrolatum is currently the best on the market because it can reduce water loss by 99% and is unlikely to cause allergic reactions. On the downside, petrolatum is not cosmetic appealing, as it is greasy and hard to remove.
Silicones such as dimethicone are another class of occlusive agents. The main advantage of silicones is their non-greasy nature, which makes them a good base for “oil-free” moisturizers.
Other occlusives used in moisturizers include beeswax, lanolin, mineral oil, paraffin, soybean oil and zinc oxide.
Humectants are substances that improve hydration by drawing water from the inner layers of the skin to outer layers. This process fills the gaps in the stratum corneum, restoring smoothness. These substances can also absorb water from the air, but this is an unwanted effect as it causes the moisturizer to become sticky and is not aesthetically pleasing.
Humectants alone are not sufficient to restore hydration because the water drawn from the deeper skin could evaporate after reaching the surface. The addition of occlusive agents to a preparation with humectants ensures water retention by preventing evaporation.
Glycerin is the most effective humectant, but should not be used alone or by people with sensitive skin. High concentrations of glycerin cause water loss from the skin, rather than improve hydration. Other humectants include propylene glycol, sodium hyaluronate, glycolic acid, lactic acid, sorbitol and urea.
3. Emollients and bath oils
Emollients are small oily elements that fit between skin cells and seal moisture, making the skin feel soft and smooth. Substances with emollient properties include castor oil, cocoa butter, coconut oil, vitamins A and E as well as other oils and fats.
Emollient ointments have effects that last longer than other formulations such as cream and lotions but are not ideal for use on the face because they are greasy. Some experts recommend adding low-potency topical corticosteroid to emollients to treat the most severe cases of dry skin.
Bath oils are another moisturizing method. Colloidal oatmeal baths allow the formation of a protective coat over the skin. This physical layer prevents water evaporation and has a moisturizing effect.
4. Barrier repair agents
The first step of skin repair in our body is the production of ceramides. This notion has inspired the creation of repair creams that contain ceramides and other molecules that mimic the natural composition of our skin. These formulations proved effective in the treating atopic dermatitis and paved the way for ceramide-based moisturizers. Cholesterols and fatty acids are other substances used in barrier repair formulations.
The cosmetic industry considers protection from sun radiation a form of moisturization. The claim is based on the thinking that sunscreens prevent dehydration by preventing damage to our skin cells. For this reason, sunscreens may be included in moisturizers that claim repair and replenishing properties.
Dry skin is an unpleasant condition caused by loss of water by evaporation. Treatment options include self-remedies as well as therapeutic products such as moisturizers.
While there is an overwhelming number of commercially available products, most contain similar basic components. In this review, we have discussed dermatologically relevant moisturizer ingredients. The choice of a specific product might take into account factors such as the application site and the severity of the issue.
Written by Raffaele Camasta, PhD
- Draelos, Z. D. (2018). The science behind skin care: Moisturizers. Journal of Cosmetic Dermatology, 17(2), 138–144.
- CPS [Internet]. Ottawa (ON): Canadian Pharmacists Association; c2018 [cited 2018 Dec19]. Dry Skin. Available from:http://www.e-cps.ca
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