The signs and symptoms of allergies include:

• itchy, watery eyes
• red eyes (conjunctivitis)
• sneezing
• coughing
• runny nose (rhinitis)
• stuffy nose
• sore throat (especially after waking, due to post-nasal drip and mouth-breathing)
• asthma symptoms: shortness of breath, coughing and wheezing

When exposure to an allergen occurs through touch or ingestion, symptoms can vary from itching, hives, flushed appearance, runny nose, and nasal congestion to more severe reactions which can cause nausea, vomiting, abdominal pain, trouble breathing, and difficulty swallowing due to swelling of the face and tongue (angioedema).

An extremely severe allergic reaction can cause anaphylactic shock, a condition in which widespread release of histamine throughout the body leads to a huge drop in blood pressure and loss of consciousness. This is often accompanied by other symptoms of a severe allergic reaction such as those mentioned above (angioedema, nausea, difficulty swallowing and breathing). This is an emergency and can lead to death if left untreated, but deaths from anaphylactic shock are not common: in the U.S. fewer than 1,000 people die each year from anaphylaxis.