1.What is skin barrier? In a broad sense, the barrier function of skin not only refers to its physical barrier effect, but also should include the pigment barrier effect of skin, nerve barrier effect, immune barrier effect and many other aspects related to skin function; in a narrow sense, the barrier function of skin usually refers to the physical or mechanical barrier structure of epidermis, especially the stratum corneum, also known as the permeability barrier. The stratum corneum of the skin is located in the outermost layer of the epidermis and was once thought to be a structure formed by useless dead cells. Recent studies, however, have revealed that keratinocytes and their extracellular components are closely embedded with each other and provide a permeable barrier to the body. The skin barrier is often compared to a “brick wall” structure, with keratinocytes as the “bricks” of the wall and intercellular lipids as the “mortar” of the wall, which tightly It connects the keratinocytes tightly, so that the skin barrier is normal, ensuring that it does not lose water and is not invaded by the outside world. At the same time, there is a layer of water-lipid film covering this brick wall structure, which together with the brick wall structure constitutes the physical barrier of the skin. 2.What happens when the skin barrier is damaged? When the skin barrier is damaged, the resistance to external pathogenic microorganisms is weakened, which will induce and aggravate many skin diseases. After the skin barrier is damaged, necrotic keratin-forming cells release damage-related molecules to activate the natural immune system and induce skin inflammation. In addition, epidermal Langerhans cells induce immune tolerance, while dermal dendritic cells have immune activation. Therefore, when the skin barrier function is intact Langerhans cells recognize cutaneous commensal bacteria without causing an immune response, but after the skin barrier function is impaired, commensal bacteria such as bacteria, fungi and viruses, which are not normally pathogenic on the skin surface, enter the dermis, are recognized by dendritic cells, present commensal antigens, activate the immune system and induce inflammation. Therefore, when the skin barrier function is damaged, it can aggravate many immune-related skin diseases such as eczema, atopic dermatitis, psoriasis, etc. 3. Focusing on moisturizing can effectively protect and improve the skin barrier. The normal skin water content is 20% to 35%, when the skin water content is reduced to less than 10%, the skin barrier function is damaged. Many skin diseases such as senile pruritus, atopic dermatitis, psoriasis, acne and dry skin are related to the decline of skin barrier function. Therefore, moisturization is crucial for the skin. Decreased skin moisturizing ability will lead to decreased skin barrier function, and decreased skin barrier function will further lead to decreased skin moisturizing ability, thus creating a vicious circle. Therefore, for normal skin barrier function moisturization is an important part of maintaining skin physiological function, delaying skin aging, and preventing and treating skin diseases. Moisturization is both fundamental and of utmost importance. The lipid mixture moisturizer can effectively relieve the symptoms of dermatitis and eczema while correcting the skin barrier function, and the restoration of skin barrier function is also beneficial to the prevention and control of local bacterial skin infections. Excessive washing, however, can remove the sebum of the skin and destroy the hydration film barrier on the skin surface, resulting in dry skin and increased transdermal water loss, thus forming the basis for the onset of pruritus senileus. Excessive washing in patients with oily skin and acne can also lead to loss of lipids on the skin surface and increased transdermal water loss, causing dry skin.