The Common Cold is a fictional character and a villain in . He is perpetually ill and wishes to eliminate the Kids Next Door and to spread his cold to the world. He uses a machine to fire mucus from his nose at the Kids Next Door. The Common Cold can normally be defeated with orange juice.

An allergy is a immune malfunction whereby a person's body is hypersensitised to react immunologically to typically nonimmunogenic substances. When a person is hypersensitised these substances are known as allergens. The word allergy derives from the Greek words allos meaning "other" and ergon meaning "reaction" or "reactivity". Reactions can vary from the benign runny nose, to life-threatening anaphylactic shock and death.