They have various causes. You get a cold when a little creature called a virus, gets into your body. Many types can get you ill.
When a cold virus gets inside you, your immune system, the body's guard against germs, dispatches a counter-assault. It's this reaction that welcomes on the classic symptoms like cough or stuffed up nose.
It's a different thing with allergies. They're brought about by an overactive immune system. For reasons unknown, your body errors harmless things, like pollen or dust, for germs and mounts an attack on them.
When that occurs, your body discharges chemicals, like histamine, similarly as it does when battling a virus. This can cause swelling in the paths of your nose, and you'll begin coughing and sneezing.
In contrast to colds, hypersensitivities aren't infectious, however, a few people may acquire a tendency to get them.