Most colds are caused by rhinovirus infection, perhaps facilitated by chilling or stress. Virus infection begins in the nasopharynx and causes spotty destruction of the nasal ciliated epithelium. Transmission occurs chiefly via droplets of various sizes transported through the air, but some types of virus persist in moist secretions on handled objects and may retain their infectiousness. Living in crowded, poorly-ventilated quarters facilitates transmission. Not many virus particles survive in saliva and it is difficult to infect via the lips or mouth. Kissing does not efficiently spread cold infection. Prophylactic treatment with interferon does not protect against cold infection. Aspirin and acetaminophen reduced serum antibody response and increased nasal symptoms in a controlled Australian study. The combination of intranasal interferon and ipratropium with oral naproxen gave promising results in experimental rhinovirus inoculation. Basically, there has been little or no progress towards effective cold treatment in the past century.