An acute viral infection caused by the herpes simplex virus type 1 and characterized by blisters in or around the mouth and lips. Orolabial herpes may or may not be related to genital herpes. Initially, the infection causes symptoms that include swelling, burning, or soreness in areas inside the mouth and on the outer skin surfaces of the mouth and lips. Clusters of tiny blisters with red bases then erupt on the hard palate, gums, or border of the lip. The throat may also be involved. The blisters break and produce irregular, red ulcerations with swollen borders. The broken blisters eventually begin to crust over.