Exclusion criteria: <br>· Multiple simultaneous lesions<br>· Area of herpes labialis involves greater than 1,5 cm in diameter<br>· Lesions that had already formed a crust<br>· Cytotoxic, immunosuppressive or immunomodifying drugs within 3 month<br>· Use of an anti-viral medication in the preceding 30 days<br>· Any evidence of active malignancy, within 3 month prior to enrollment (subjects who have completed therapy and are considered unlikely to relapse or who have had surgery and do not have any evidence of disease, are eligible for the study)<br>· Female patients who are pregnant and/or nursing or planning a pregnancy<br>· Females of childbearing potential, with positive urine pregnancy test at time of screening<br>· Congenital, acquired or corticosteroid-induced immunodeficiency<br>· History of allergic or adverse response to acyclovir, or any related anti-viral drug, or the cream base<br>· History of intolerance or hypersensitivity to chloramine-T, or other ointment components<br>· Current significant skin disease within the affected area<br>· Use of topical medications in the affected area within 72 hours prior to study enrolment<br>· History of positive result for hepatitis B surface antigen, hepatitis C virus, or HIV<br>· No participation in another clinical drug research study 1 month before inclusion, during the study and at least 1 month after the study end <br>· Allergy for any drug or idiosyncrasy (excludes a pollen allergy without current symptoms) <br>· Having exanthem, pigment abnormality, other skin symptoms such as wounds and/or an excessive sunburn in the affected area<br>· Abnormal skin conditions that occur in the area ordinarily affected by cold sores which might affect the normal course of cold sores (e.g. eczema, psoriasis, albinism, or chronic vesiculobullous disorders) <br>· History of clinically significant itching, erythema and/or rash by any locally applied treatment<br>· Unreliability or unability to understand or follow the protocol directions or to comprehend or satisfactorily use the measurement scales as determined by investigator or designee at screening<br>