Thermal burns usually result from placing hot food or beverages in the mouth. This may occur in those who eat or drink before a local anesthetic has worn off. The normal painful sensation is absent and a burn may occur. Microwave ovens sometimes produce food that is cold externally and very hot internally, and this has led to a rise in the frequency of intra-oral thermal burns. Thermal food burns are usually on the palate or posterior buccal mucosa, and appear as zones of erythema and ulceration with necrotic epithelium peripherally. Electrical burns more commonly affect the oral commissure (corner of the mouth). The lesions are usually initially painless, charred and yellow with little bleeding. Swelling then develops and by the fourth day following the burn the area becomes necrotic and the epithelium sloughs off.