Rhinoviruses (from the Greek (gen.) "nose") are the most common viral infective agents in humans and are the predominant cause of the common cold. Rhinovirus infection proliferates in temperatures between 33–35 °C (91–95 °F), the temperatures found in the nose. Rhinovirus is a species in the genus Enterovirus of the Picornaviridae family of viruses.
There are 99 recognized types of human rhinoviruses that differ according to their surface proteins. They are lytic in nature and are among the smallest viruses, with diameters of about 30 nanometers. By comparison, other viruses such as smallpox and vaccinia are around 10 times larger at about 300 nanometers.