Introduction

The skin is the largest organ of the human body. In an average-size adult, it covers a total area of about 20 square feet. Forming the outer boundary of the body, the skin performs several essential functions: it acts as a barrier to protect vital internal organs from infection and injury, helps to dissipate heat and regulate body temperature, and synthesizes vitamin D when exposed to ultraviolet (UV) light. In addition, various sensory receptors present throughout the skin enable it to respond to such sensations as heat, cold, pain, and pressure.
The specialty of dermatology deals with the skin and its accessory structures: hair, nails, and sweat glands, and the subcutaneous tissue that lies beneath the skin. A physician who specializes in dermatology is called a dermatologist.