To better understand skin foreign body, 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.
- Nassif JM, Gorczyca JT, Vanarthos WJ. Unrecognized foreign body in the hip joint. J Orthop Trauma. 1996;10(3):216-9. 
- O'Dell ML. Skin and wound infections: an overview. Am Fam Physician. 1998 May 15;57(10):2424-32. 
- Vincent A, Jenkins DW. Retained digital foreign body after a pellet gun injury. J Am Podiatr Med Assoc. 2000 Feb;90(2):103-6.