The skin is considered the largest organ of the body and has many different functions. The skin functions in thermoregulation, protection, metabolic functions and sensation. The skin is divided into two main regions, the Epidermis, and the Dermis, each providing a distinct role in the overall function of the skin. The dermis is attached to an underlying hypodermis, also called subcutaneous connective tissue, which stores adipose tissue and is recognized as the superficial fascia of gross anatomy.
The layer of skin you see, the Epidermis, is made up of the cells that manufacture skin. The outer layer is dead skin cells. Underneath are flat, scale like cells called Squamous cells, and beneath them are round basal cells. The epidermis also contains cells that produce melanin, which gives skin its color. Every hair on your body grows from a live follicle with roots in the fatty layer called subcutaneous tissue. The sebaceous glands secrete sebum, an oily substance that helps keep skin from drying out. Most of the glands are located in the base of hair follicles. Acne starts when the tiny hair follicles become plugged with these oily secretions. Subcutaneous tissue, mostly made up of fat, lies between the dermis and muscles or bones, and contains blood vessels that expand or contract to help keep your body a constant temperature. Fatty tissue is distributed unevenly over your body and thins with age. The dermis contains two types of fibers that lessen in supply with age: Elastin, which gives skin its elasticity, and collagen, which provides strength. The dermis also contains blood and lymph vessels, hair follicles, sweat glands and the sebaceous glands, which produce oil.
When your body gets hot or is under stress, these glands produce sweat, which evaporates to cool you. Sweat glands are located all over the body, but are especially abundant in your palms, soles, forehead and underarms. The Apocrine glands are specialized sweat glands that emit an odor. To help keep your body a constant temperature, blood vessels in the skin dilate in response to heat or constrict in response to cold. Only your lips, palms and the soles of your feet are truly hairless. Most hair helps protect the body in some way: on the scalp, it provides some insulation and protects you from sun exposure, in eyelashes and eyebrows, it helps protect your eyes.