Skin is the largest and heaviest organ in the human body. It has several important functions, including protection from external factors (such as UV radiation, chemicals, etc.), regulation of body temperature, and sensation. The skin consists of three main layers: the epidermis (the outermost layer), the dermis (the middle layer), and the subcutaneous tissue (the innermost layer).
The epidermis is composed of stratified squamous epithelium. It provides a barrier against water loss and protects against physical, chemical, and biological agents. The thickness of the epidermis varies depending on location on the body; for example, it is thicker on the palms of the hands and soles of the feet than on other parts of the body. The dermis is composed of connective tissue and contains blood vessels, hair follicles, sweat glands, sebaceous glands, sensory receptors, and more. This layer provides structural support for the skin and helps to regulate body temperature. The subcutaneous tissue is composed primarily of adipose tissue (fat). This layer attaches the skin to underlying structures such as muscles and bones.
Skin color is determined by a number of factors including pigmentation (melanin production), blood flow, carotene levels, etc. Skin can be affected by a variety of diseases or conditions including acne, eczema, psoriasis, dermatitis herpetiformis , vitiligo , cuts/bruises , sunburn , frostbite , cancer , etc. Proper skincare is important for maintaining healthy skin; this includes cleansing , exfoliation , moisturizing , protecting from UV radiation , etc.