The Integumentary System is a collection of organs that constitute the body’s external covering and defend it against a variety of hazards including infection, dehydration, abrasion, chemical assault, and radiation damage. The skin, a thickened keratinized epithelium comprised of numerous layers of cells that is essentially impermeable to water, is part of the integumentary system in humans. It also contains immune cells and specialized cells that secrete melanin to protect the body from the cancerous effects of UV radiation. The integumentary system also includes sweat glands, which expel waste and control body temperature.