No kidding! This CDC photograph captured a sneeze in progress, revealing the plume of salivary droplets as they are expelled in a large cone-shaped array from this man's open mouth. The flu virus can spread in this manner and survive long enough on a doorknob or countertop to infect another person. It dramatically illustrating the reason you should cover your mouth when sneezing or coughing to protect others from germ exposure, health officials say. It
Credit: CDC/James Gathany
An allergy is a reaction of your immune system to what are usually harmless, run-of-the-mill substances that most people's bodies don't perceive as dangerous. The offending substance, called an allergen, can take many forms, from cat hair to pollen to penicillin.
While allergies can result in a range of symptoms, from wheezing and sneezing to itching, swelling and rashes, these seemingly diverse afflictions all have a common cause.
Let's say you're allergic to peanuts. When you eat a peanut, your body sees the allergen as a threat. Your immune system then sends out an alarm as though it is being attacked by an infectious invader.
First, your immune cells produce Y-shaped proteins called antibodies. These antibodies bind to the allergen, like a lock and key. The occupied antibody can then go and attach to specific cells known as mast cells, which trigger the release of chemicals like histamine that cause allergic symptoms.
It's helpful to think of the antibody as hooked to a piñata, said Dr. Jacqueline S. Eghrari-Sabet, an allergist at Family Asthma & Allergy Care in Gaithersburg, Md. "That piñata busts open and out comes a whole bunch of chemicals that your body makes, and makes you sneeze and wheeze and itch and break out in hives."
A large part of why certain people have allergies to certain things has to do with their heredity. Some people's bodies are genetically prone to sending out false alarms to things like pollen and animal hair.
Also, in order to develop an allergy to something, you have to have been exposed to it before. That is, if you've never come into contact with peanuts, you won't have an allergic reaction the first time you eat them, but you can after subsequent exposures.
Studies show that allergies, especially those to food, have been on the rise in recent years, though no one is quite sure why. Some have suggested that modern societies are simply too clean, leading our bored immune systems to attack seemingly harmless things. Others think global warming could be partly to blame as well, with the rise in temperatures and carbon dioxide causing a boon in plant growth and, subsequently, pollen production. However, both of these hypotheses remain difficult to prove.