The common cold is an acute (short-term) viral infection of the upper respiratory tract that may be spread through the air, for example, by sneezing, or by contact with contaminated objects. Influenza, or the “flu,” is the name of a virus and the infection it causes. Although for most people the infection is mild, it can be severe and even deadly in those with compromised immune systems. Allergies are responses mounted by the immune system to a particular food, inhalant (airborne substance), or chemical. The following conditions are related to cold, flu, and allergy. The Allergies and Sensitivities article also contains a list of health conditions that may be allergy related.