Allergic reactions are a type of immune system response that occurs when the body is exposed to a foreign substance, such as pollen or pet dander. Common allergic reactions include rashes, sneezes, and achoos. Rashes are an inflammation of the skin that can cause redness, itching, and swelling. Sneezes are a sudden, involuntary expulsion of air from the nose and mouth. Achoos are a series of sneezes in quick succession. Allergic reactions can range from mild to severe and can be treated with medications or lifestyle changes.