The skin, also known as the cutaneous membrane or integument, is the largest organ of the body by weight. It forms a protective barrier between the internal environment and the external world.

Functions of the skin include:

• Protection from injury and infection
• Regulation of body temperature
• Sensation of touch, pressure, pain, and temperature
• Synthesis of vitamin D
• Excretion of waste products

Skin appendages, also known as accessory structures, are structures that develop from the embryonic epidermis and include:

• Hair: Provides insulation and protection. Source
• Nails: Protect the tips of fingers and toes and aid in grasping objects. Source
• Sweat glands: Produce sweat to cool the body through evaporation. There are two main types:
  • Eccrine sweat glands: Found all over the body and produce a watery sweat. Source
  • Apocrine sweat glands: Located in the axillae (armpits) and groin and produce a thicker sweat that contains proteins and fats. Source
• Sebaceous glands: Secrete sebum, an oily substance that lubricates the skin and hair. Source