What are the layers of skin?

The skin is made up of 3 layers: the epidermis, the hypodermis, and the dermis, which vary significantly in their anatomy and function from one another. 

1. The epidermis is the top layer of the skin that one is able to see and touch. Keratin makes up the skin cells, and along with other proteins sticks together to form this layer. The epidermis has several functions such as acting as a protective barrier, making new skin, providing skin color, and protecting the body. The epidermis prevents bacteria and foreign substances that cause infections  from entering the body and bloodstream. This skin layer is heavily colonized by commensal bacterial organisms which help protect against harmful bacteria. The epidermis also makes new skin cells, which replace the approximately 40,000 old skin cells that the body sheds everyday. A human has new skin every 30 days. Additionally, the epidermis also contains melanin, which is the pigment that gives skin its color. This layer also protects the body by using Langerhans cells, which are a part of the body’s immune system. These cells help to fight off infections and bacteria. 
2. The dermis makes up 90% of the skin’s thickness and is the middle layer. Its functions include having collagen and elastin, receiving sensory information, growing hair, making oil, supplying blood, and producing sweat. Collagen is a protein found in the dermis that helps keep skin cells resilient and strong. Elastin is also found in the dermis, and helps keep skin flexible, as well as helps stretched skin regain its original shape. The dermis also processes sensory information, as the nerve receptors are able to tell if something one touches is soft, hard, or itchy. The dermis also has sweat glands which release sweat through skin pores; this helps to regulate body temperature. The dermis also grows hair, as the roots of hair follicles are able to attach to it. Additionally, this layer produces oil through oil glands, keeping the skin soft and smooth. Oil also prevents the skin from absorbing too much water during activities like swimming. Lastly, blood vessels in the dermis give nutrients to the epidermis, keeping the skin layers healthy.        
3. The hypodermis is the bottom layer of the skin, and is also known as the fatty layer. Its functions include cushioning muscles and bones, assisting the nerves and blood vessels, having connective tissue, and regulating body temperature. The fat in the hypodermis protects muscles and bones from various injuries after falling or accidents. The hypodermis also helps nerves and blood vessels from the dermis get larger and branch out to connect the hypodermis to the rest of the body. Additionally, this layer skin is able to connect layers of skin to muscles and bones through connective tissue. The fat in the hypodermis also plays a role in body temperature, as it prevents the body from being too cold or too hot.