To better understand a furuncle, it helps to understand the anatomy of the skin.
The skin contains three main layers:
- The superficial layer that makes up the surface of the skin
- It is composed of skin cells and can be divided into 5 layers based on cell type.
- The top layer of the epidermis, the stratum corneum, is made of dead, flat skin cells that shed about every 2 weeks.
- The thickness of the epidermis varies, according to location: it is very thick over the soles of the feet, and very thin over the ears.
- Lies beneath the epidermis
- Also varies in thickness depending on the location of the skin. It is .3 mm on the eyelid and 3.0 mm on the back.
- The dermis is composed of 2 layers that contain a connective tissue called collagen
- The dermis contains blood vessels, nerves, sweat glands, and hair follicles.
- The number of structures in the dermis varies, according to location.
- The dermis under the arms contains more sweat glands and hair follicles than the dermis on the back.
- Subcutaneous layer:
- Mainly fat and connective tissue.
- Contains blood vessels and nerves.
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- Laube S, Farrell AM. Bacterial skin infections in the elderly: diagnosis and treatment. Drugs Aging. 2002;19(5):331-42. 
- Winthrop KL, Abrams M, Yakrus M, Schwartz I, Ely J, Gillies D, Vugia DJ. An outbreak of mycobacterial furunculosis associated with footbaths at a nail salon. N Engl J Med. 2002 May 2;346(18):1366-71.