Abstract: An aqueous extract of Oenothera caespitosa having antiviral activity. Compositions containing such an extract are especially effective in topically treating herpes simplex lesions. Methods of making and using the extract are also disclosed. Topically applied compositions relieve pain and promote healing of lesions caused by the herpes simplex virus, varicella virus, and Epstein-Barr virus. The composition may also reduce the recurrence of herpes simplex lesions and act as a prophylactic agent by interrupting the spread of the virus and subsequent vesicle and lesion formation.