The common cold or head cold, also known as acute nasopharyngitis, was a viral Human illness of the upper respiratory system that had existed at least since Earth's Stone Age. The primary symptoms of the illness included a sore throat, coughing, and either a stuffed or runny nose. The virus was contagious, and could be spread by both direct contact and droplet infection. They were caused by Rhinoviruses.
According to Doctor Phlox, one of the most virulent species of space-dwelling microbes, Polycocyx astris, was able to drift in a dormant state for millions of years and could still cause a nasty cold. (ENT: "Breaking the Ice")
In 2151, Malcolm Reed was surprised that, although Humans could travel past light speed, they still could not cure the common cold. Phlox replied that there was no cure or treatment for the illness except for methods similar to those used in the 20th century. Reed wondered how he had caught the virus inside a hermetically sealed starship, causing Phlox to suggest that he might have picked it up from a contaminated tool or a sealed container. When Reed recalled that he had opened a case of plasma coolant, Phlox surmised the coolant's packer had been nursing a cold. He dismissed Reed's protests that it had happened five months ago at spacedock, saying viruses could survive and adapt. (ENT: "Sleeping Dogs")
Doctor Leonard McCoy noted that modern medicine was still searching for a cure for the common cold in the 23rd century. (TOS: "Plato's Stepchildren") McCoy found a number of promising biological candidates on Omega IV that might lead to a viable cure. (TOS: "The Omega Glory") Scotty also mentioned that the common cold was yet uncured, comparing Mira Romaine's discomfort with space to this affliction. (TOS: "The Lights of Zetar")
In 2368, after Geordi La Forge experienced headaches and dizziness, Doctor Beverly Crusher did a parameter search for these symptoms through his file in the patient medical records database. One of the events listed in this database was when he had the common cold on stardate 45773.0, for which he suffered headaches from. (TNG-R: "Cause and Effect")
Tom Paris once told The Doctor that when he was nine years old, he had a cold. His childhood doctor, Dr. Brown, who still made house calls, "whipped up a pot of garlic soup and brought it over himself." (VOY: "Cathexis")