The epidermal skin barrier, primarily located in the outermost layer known as the stratum corneum, is the body’s first line of defence against the external environment. It is a complex structure composed of dead skin cells (corneocytes) embedded in a matrix of lipids, including ceramides, cholesterol, and fatty acids. This “bricks and mortar” arrangement is crucial for preventing the loss of water and electrolytes from the body and for blocking the entry of harmful substances, irritants, and microorganisms. Understanding the structure and function of this barrier is paramount in cosmetic dermatology, as it dictates how cosmetic products interact with the skin and how they can be used to support its health.
Cosmetic products can impact the epidermal barrier in various ways, both positively and negatively. Harsh chemicals, abrasive scrubs, and cleansers that are too alkaline can disrupt the lipid matrix, leading to a compromised barrier. This disruption can result in increased transepidermal water loss (TEWL), causing dryness, dehydration, and increased sensitivity. A weakened barrier also makes the skin more vulnerable to irritation from environmental factors and the penetration of potential allergens and pathogens.
Conversely, many cosmetic products are specifically formulated to support and enhance the epidermal barrier function. Moisturisers are central to this. They typically contain a combination of ingredients that work through different mechanisms to improve hydration and barrier integrity.
Occlusives, such as petrolatum and mineral oil, form a protective film on the skin surface, physically blocking water from evaporating.
Humectants, like glycerin and hyaluronic acid, attract and bind water within the stratum corneum, increasing its hydration levels.
Emollients, which are often lipids and oils, help to fill the gaps between corneocytes, smoothing the skin surface and improving barrier function by creating a more cohesive structure.
By replenishing lipids and improving hydration, moisturisers help to repair a compromised barrier, reduce TEWL, and restore the skin’s ability to protect itself. This is particularly important for individuals with dry skin or skin conditions like eczema and atopic dermatitis, where the barrier function is inherently impaired.
Cleansers also play a crucial role in supporting the skin barrier. As mentioned previously, the choice of cleanser is vital. Mild, pH-balanced cleansers that do not strip the skin of its natural oils are essential for maintaining barrier integrity. Synthetic detergent (syndet) bars are often preferred over traditional soap bars, as they tend to be less alkaline and less disruptive to the skin’s natural pH and lipid content. By cleansing gently and effectively, these products help to remove impurities without compromising the barrier’s protective function.
Certain active ingredients found in cosmetic products can also contribute to a healthy skin barrier. Niacinamide (a form of vitamin B3) has been shown to enhance the production of ceramides, key lipids in the stratum corneum, thereby strengthening the barrier and reducing TEWL. Panthenol (pro-vitamin B5) is another ingredient that can improve skin hydration and support barrier repair. Antioxidants, while primarily known for their protective effects against free radical damage, can indirectly support barrier function by preventing damage to skin cells and lipids. The development of novel delivery systems in cosmetic products also aims to enhance the effectiveness of barrier-supporting ingredients. Liposomes, nanoparticles, and other advanced formulations are designed to improve the penetration of active ingredients into the skin, allowing them to reach the layers where they can exert their beneficial effects on barrier function.