The common cold is the most prevalent disease in humans. It is generally caused by rhinovirus. Bacterial involvement is rare, and an uncomplicated common cold does not require treatment with antibiotics. The symptoms are not caused by tissue destruction, but rather by the response of the immune system, including the release of kinins and interleukins. The intensity of transmission depends upon the amount of nasal discharge. It is mediated in part by the hands (sometimes via contaminated objects) and partly by aerosols. Rhinovirus is involved in 40% of asthma attacks in school children, and in about 60% of exacerbations in adults with chronic obstructive pulmonary disease. Smoking, stress, and a few types of social contact are all risk factors, whereas alcohol consumption seems to be protective. Exposure to a cold environment is probably of no significance in the pathogenesis. No effective cure is known. The medications in use are all directed exclusively against the symptoms, and especially for pre-school children, they are of doubtful value and potentially harmful.