Phase 3 Clinical Study for the Treatment of Cold Sore

Inclusion Criteria: * History of recurrent herpes labialis lesions where: * At least 50% of previous episodes produced classical lesions to the vesicular stage (i.e. episodes that progressed through macula, papule, vesicle, crust and healed); * Prodromal symptoms (itching, tingling, pain etc.) should precede herpes labialis lesions in at least 50% of the previous herpes episodes * Good general health (ECOG \< 2), immunocompetent * Signed and dated written informed consent * Women of childbearing potential must have effective contraception method Exclusion Criteria: * More than 50% of recurrences that aborted spontaneously in the past 12 months * Primary herpes lesion outside the lips (e.g. nose, chin, etc.) * Abnormal peri-oral skin condition that might affect the normal course of cold sores (e.g. eczema, psoriasis…) * Oral diseases whose prodromal symptoms may mimick those of herpes labialis, including recurrent oral aphthous disease * Oral diseases that might interfere with the evaluation of the efficacy or safety of the treatments, including gingivitis, parondotis, mucositis, oropharyngeal candidiasis… * History of infection known to be resistant to acyclovir family agents * Previous vaccination against herpes * Concomitant treatment likely to interfere with acyclovir * Allergy to any acyclovir containing agents * Immunocompromised condition, including HIV+ * Unability to properly understand protocol requirements, to follow the study procedures, to complete the patient diary or to start the self-initiation of the treatment * Upper full or partial dentures with acrylic border in the canine fossa * Milk allergy or known history of hypersensitivity to one of the components of the products * Rare hereditary problems of galactose intolerance. * Lactase enzyme deficiency or glucose galactose malabsorption * Clinically significant abnormal level of serum creatinine * Patients whose occupations make them unlikely to return to the clinic within 24h of treatment initiation * Pregnancy or breast-feeding * Investigational drug or immunomodulator treatment in the 30 days prior randomisation * Prior enrollment in this study * Participation in another therapeutic trial evaluating new drugs or which could interfere with the evolution of herpes labialis or the evaluation of the drug in the study within preceding 30 day.