The Common Cold remains the most frequent symptomatic viral infection in man. Current best therapies are all symptomatic. New pharmacological therapies are likely to be prescription-bound, and as most Common Cold infections are successfully treated without the intervention of a Physician, there is a need for effective non-prescription therapy options. Aim of this study is to propose a new type of approach, based on the concept of making a hostile biological environment for virus survival and spreading at the point of infection, the nasopharynx. The hypothesis was advanced that infections could be controlled using a physical biological approach to create an environment at the point of infection, that is inhibitory to the survival, and persistence of infecting virus, and of viruses newly released from infected mucosal epithelial cells. A nasal irrigation spray, designed to deliver a low pH gel to the nasal cavity, was developed and tested in this study. The study was a randomised, parallel, double-blind, placebo-controlled evaluation of three formulations of irrigation nasal spray in 441 subjects. The objective was to test whether the formulations reduced Cold severity and Cold duration compared to a placebo nasal spray. Subjects were recruited, and supplied with the product when healthy, and were instructed to begin treating and recording symptom severity once they experienced the "first signs" of a Common Cold. To qualify, subjects had to volunteer that they had at least one of the symptoms: sore/scratchy throat, runny nose or congested nose. The product was used 4 times daily, with at least 4 hours separating each dose, for a maximum of 7 days. Efficacy was assessed by an Interactive Voice Recall System whereby subjects were required to contact the investigation site, by telephone, twice daily when they were asked to assess the severity of their symptoms using a four point ordinal scale where 0 = "absent", and 3 = "severe". The symptoms assessed were sore throat, runny nose, blocked nose, cough and tired/run-down feeling. Two formulations demonstrated significant effects. A hydroxy methyl propyl cellulose based formulation reduced symptom severity compared with placebo by 17% and a Poloxamer based formulation reduced severity by 21%. Duration of illness was reduced with a hydroxy methyl propyl cellulose based formulation by 1.5 days to 2.4 days (according to the dose) and by a Poloxamer based formulation by 2.5 days. Results of this study suggest that the creation of a non virus-specific, inhibitory environment in the nasopharynx holds promise as an effective method of controlling the severity and duration of the Common Cold.