If there is a champion among contagions, it may well be the lowly rhinovirus, responsible for many of the coughs and sniffles that trouble us this time of year. Rhinoviruses are spectacularly effective at infecting humans. Americans suffer one billion colds a year, and rhinoviruses are the leading cause of these infections.

Scientists have never been sure why they are so effective, but now a team at Yale University may have found a clue. The scientists argue that rhinoviruses have found a blind spot in the human immune system: They take advantage of the cold air in our noses.

In the 1960s, researchers first noticed that if they incubated rhinoviruses a few degrees below body temperature, the viruses multiplied much faster. It was an intriguing finding, since rhinoviruses often infect the lining of the nostrils, which are cooled by incoming air.

In subsequent years, scientists searched for an explanation. “People have taken the virus apart and studied its parts,” said Akiko Iwasaki, an immunobiologist at Yale. “But none of this really added up to explain why the virus replicated faster at a lower temperature.”