What are the nonliving parts of skin?

The nonliving parts of skin include:

- Keratin: A tough, waterproof protein that makes up the outermost layer of skin (the epidermis). Keratin also makes up hair and nails.

- Collagen: A strong, fibrous protein that provides strength and elasticity to the skin. Collagen is also found in bones, tendons, and ligaments.

- Elastin: A stretchy protein that allows skin to stretch and then return to its original shape. Elastin is also found in lungs and blood vessels.

- Hyaluronic acid: A glycosaminoglycan that helps keep skin hydrated and plump. Hyaluronic acid is also found in cartilage and synovial fluid.

- Sebum: An oily substance produced by the sebaceous glands. Sebum helps to keep skin moisturized and protected from the elements.