Let's first get to know the skin. The physiological functions of the skin can be summarized into six aspects, and each aspect will directly or indirectly affect whitening when there is a problem: 1. You protect your skin, and it protects you. The skin constitutes the first line of defense for the human body, not only having protective effects against mechanical, physical, chemical, bacterial and other microorganism damages, but also preventing the loss of nutrients and water in the body. Normal skin has the ability to absorb light, and the melanin produced by the melanocytes in the basal layer can absorb ultraviolet rays, playing a protective role in preventing sunburn damage caused by ultraviolet rays. 2. Secretion and excretion functions. The secretion and excretion functions of the skin are mainly completed through sweat glands and sebaceous glands. Sebaceous glands secrete sebum to lubricate the skin and inhibit the growth of certain pathogenic microorganisms. However, if the seborrheic areas with more sebaceous glands are not thoroughly cleaned, acne and rosacea may easily occur, leaving pigmentation spots and scars after healing, affecting the whitening of the skin. 3. Absorption of nutrients. The skin has the ability to absorb external substances, which is the basis for skin beauty care and topical drug treatment of skin diseases. Various whitening cosmetics also use the absorption capacity of the skin to achieve the effects of removing spots, whitening, and beautifying. 4. Regulating body temperature. There are many temperature receptors distributed in the skin that can sense changes in environmental temperature. Under the action of the body temperature regulation center, the body maintains a constant temperature through the contraction and dilation of blood vessels in the skin, shivering, sweating, etc. If the skin is exposed to cold or heat stimulation for a long time, it can cause dysfunction of the vasodilation and vasoconstriction in the dermis, leading to skin diseases such as erythema and chilblains. Pigmentation spots may remain after healing, disrupting the perfection of the skin. 5. Metabolic function. The skin has the metabolic capacity of various substances such as carbohydrates, proteins, and lipids. Abnormal pigment metabolism in the skin can lead to pigmented skin diseases such as freckles, melasma, and pityriasis alba. In addition, how are eye bags formed? The skin can synthesize glycogen, and if the skin metabolism is abnormal, the glycogen content will increase, favoring the proliferation of bacteria and other pathogenic microorganisms, making the skin prone to infection and leaving scars after healing. 6. Immune function. There are various immune-related cells in the skin tissue, which can produce immune reactions to bacteria, viruses, etc., that come into contact with or enter the skin surface, protecting the body from invasion by pathogenic microorganisms. If the immune-related cells of the skin are abnormal, various skin diseases may occur, leaving pigmentation and scars after healing, which are disharmonious notes for whitening.