Barrier replenishing ingredients are those that help restore the skin’s natural barrier. The outermost layer of skin, known as the stratum corneum, acts as a primary barrier between the body and its environment. The stratum corneum is composed of dead skin cells known as corneocytes that are held together by a lipid matrix. The lipid matrix contains about 50 percent ceramides, 25 percent cholesterol, and about 10 to 15 percent fatty acids.
Without these essential lipids, the barrier is weakened. A weak or damaged barrier leads to transepidermal water loss (TEWL) and may allow harmful things like allergens, bacteria, and irritants to pass through into the deeper layers of skin. This can lead to symptoms of dryness, itching, and irritation, and may eventually cause skin conditions such as acne, eczema, sensitive skin, and even signs of aging. Ingredients that help replenish the skin’s barrier function, such as ceramides, cholesterol, and fatty acids, are classified as barrier replenishing ingredients.