Skin biology is the study of the skin, the largest organ of the human body. It serves as a protective barrier against environmental factors, regulates temperature, and enables the sensation of touch. The skin consists of three main layers: the epidermis, dermis, and hypodermis, each with distinct functions and structures. The epidermis contains cells that produce keratin, which helps protect against water loss and pathogens. The dermis houses blood vessels, nerves, and connective tissue, providing strength and elasticity. The hypodermis connects the skin to underlying tissues and stores fat for insulation and energy. Understanding skin biology is essential for skincare and medical treatments.