Cold sores, also called fever blisters, are tiny, fluid-filled lesions that occur on and around your lips. These blisters are often grouped together in patches and are caused by the Herpes Simplex Virus (HSV) Type I. The blisters are most commonly found around the mouth area and are usually painful. They may last from 1 to 2 weeks before resolution and may slowly evolve into a crusted bump. Fever blisters spread from person to person by close personal contact. There’s no cure for HSV infection; therefore, the blisters may recur sporadically due to stress, sunburn, or physical trauma. Topical and oral treatment are quite effective in hastening the resolution of this condition, but patients who are chronically plagued by herpes simplex, maintenance therapy with Acyclovir is recommended.