MEDICAL ANIMATION TRANSCRIPT: Your doctor may obtain a skin biopsy to view the tissue under a microscope, and make a diagnosis of your condition. The skin is the largest organ of the body, and is responsible for regulating body temperature; sensing painful and pleasurable stimuli; providing a protective barrier against bacteria, toxins, and extreme temperatures; and maintaining a balance of water and electrolytes by preventing internal fluid evaporation. Skin consists of three layers: the epidermis, dermis, and hypodermis. The epidermis helps prevent most bacteria and other foreign substances from entering the body. The dermis provides support for the epidermis, and gives the skin its flexibility and strength. The hypodermis is a layer of fat cells providing insulation and protective padding. Skin biopsies are commonly ordered for warts and moles, skin cancers and other growths, allergic reactions, bacterial or fungal infections, acne, psoriasis, and injuries and scarring. For all skin biopsy procedures, your doctor will inject your skin with a local anesthesia to numb the area. Shave biopsies are usually performed on surface lesions. During this procedure, your doctor will use a sharp scalpel or razor blade to thinly slice or shave the top layer of the skin lesion. This type of biopsy does not require stitches. Doctors usually perform a punch biopsy for deeper skin lesions. Your doctor will rotate a circular, hollow blade around the lesion until it cuts completely through the epidermis and dermis. He or she will remove a small cylinder of skin-- usually smaller than the size of a pencil eraser-- containing all layers of the skin lesion. Depending on the size of the sample, the area may or may not be closed with stitches. An excisional biopsy is larger and deeper than a shave or punch biopsy. It is used for conditions such as cancer, which must be entirely removed. Your doctor will go as deep as is necessary to remove all of the area visibly affected, as well as some unaffected tissue around the outside of the lesion. The incision is then closed with stitches. After the biopsy, you will need to keep the area dry, and cover it with a sterile bandage or gauze dressing for one to two days. Antibiotic ointment should be applied until it is completely healed. Acetaminophen or ibuprofen can be taken for any discomfort at the biopsy site.