This trial is a double-blind, multicenter, placebo-controlled clinical trial. Participants are randomized to topical 15% SP-303 gel and oral acyclovir or to matching topical placebo gel and oral acyclovir. At presentation, patients are stratified by total lesion area within each treatment group. SP-303 or matching placebo is topically applied three times a day until all lesions are reepithelialized or for 14 days, whichever occurs earlier. Acyclovir is administered by mouth each day, three times a day, until all lesions are reepithelialized or for 14 days, whichever occurs earlier. Patients are evaluated for lesion healing and adverse events 3 times per week during the treatment period. The primary efficacy endpoint will be complete lesion healing and the primary analysis will be time to complete healing.