Which layer of the skin is primarily composed of cells?

The epidermis is the outermost layer of the skin and is primarily composed of cells, specifically keratinocytes, which make up about 90% of the epidermis. These cells form a protective barrier against environmental factors and pathogens. The epidermis also contains melanin-producing cells, known as melanocytes, which give skin its color as well as Langerhans cells that play a role in the immune response.

The other layers of the skin serve distinct purposes but are not primarily made of cells in the same way as the epidermis. The dermis, for instance, is mainly composed of connective tissue, which includes a matrix of collagen and elastin fibers, and contains blood vessels, nerves, hair follicles, and glands. The hypodermis and subcutaneous layer, while related to the skin, are predominantly composed of fat and connective tissue and serve as insulation and cushioning for the body, rather than being made up of a dense layer of cells like the epidermis. This composition makes the epidermis unique in its primary function of protection and regeneration.