Overview
An allergic reaction begins when the body's immune system treats a substance as harmful even though it may not be dangerous to most people. This can lead to symptoms in one part of the body, such as a rash or sneezing, or in several body systems at once. Reactions may happen within minutes or develop more slowly, depending on the trigger.
Key Symptoms
Mild symptoms may include itching, hives, rash, runny nose, sneezing, watery eyes, nausea, or mild swelling. More serious symptoms include swelling of the lips, tongue, or throat, wheezing, trouble breathing, repeated vomiting, dizziness, confusion, or fainting. Symptoms can worsen quickly, especially with food, medicine, or insect-sting allergies.
Causes and Risk Factors
Common triggers include certain foods such as peanuts, tree nuts, milk, egg, shellfish, wheat, and soy; medicines such as antibiotics; insect stings; latex; and environmental allergens like pollen, dust mites, or animal dander. A personal or family history of allergies, asthma, or eczema can raise the chance of allergic disease. Having had a previous allergic reaction may increase the risk of another reaction to the same trigger.
Who Is Affected
Allergic reactions can happen at any age, from infancy through older adulthood. Some allergies are more common in children, while medicine allergies and severe reactions can occur at any stage of life. People with asthma may be at higher risk of severe breathing problems during an allergic reaction.
Prevention
The most important step is to avoid known triggers as much as possible. Read food labels carefully, ask about ingredients when eating away from home, and tell healthcare workers about any past reactions to medicines, latex, or contrast materials. If a healthcare professional has given you an allergy action plan or emergency medicine device, keep it available and make sure family, school, or workplace contacts know how to respond.
Diagnosis and Tests
A healthcare professional may ask about what happened, how quickly symptoms started, possible triggers, and any history of asthma, eczema, or past reactions. Diagnosis may involve a physical exam and, when appropriate, referral for allergy testing such as skin tests or blood tests. Do not try to test a suspected trigger on your own after a serious reaction.
Treatment Categories
Treatment depends on how severe the reaction is and which body systems are affected. Mild reactions may be managed with monitoring and treatments recommended by a healthcare professional, while severe reactions need emergency care right away. After a significant reaction, follow-up care can help identify triggers and make a plan to reduce future risk.
When to Seek Medical Care
Seek medical care promptly for a first-time allergic reaction, symptoms that keep returning, reactions linked to food, medicine, or insect stings, or swelling around the face or mouth. Medical advice is also important if allergies are affecting sleep, school, work, or daily activities. Follow-up is especially important after any reaction that seemed to spread beyond one body area.
When It May Be an Emergency
Get emergency help immediately if there is trouble breathing, wheezing, throat tightness, swelling of the tongue or throat, repeated vomiting, severe weakness, fainting, or sudden symptoms affecting more than one body system. These can be signs of anaphylaxis, which can become life-threatening within minutes. If emergency medicine has been prescribed for severe allergy, use it as directed by the prescribing clinician and seek emergency care right away.