Overview
Allergens are substances that can cause the immune system to overreact in people with allergies. This reaction can lead to symptoms such as sneezing, itching, rash, swelling, wheezing, or stomach upset. Allergens can be inhaled, eaten, touched, injected, or absorbed through medicines.
Key Symptoms
Symptoms depend on the allergen and how the body is exposed to it. Common symptoms include sneezing, runny or blocked nose, itchy or watery eyes, skin rash, hives, coughing, wheezing, nausea, vomiting, diarrhea, or swelling of the lips or face. A severe reaction can cause trouble breathing, dizziness, fainting, or swelling of the throat.
Causes and Risk Factors
An allergic reaction happens when the immune system responds to an allergen as though it were dangerous. Risk may be higher in people with a personal or family history of allergies, asthma, or eczema. Repeated exposure to certain substances in the home, workplace, or outdoor environment may also play a role.
Who Is Affected
People of any age can be affected by allergens, including infants, children, and adults. Some allergies begin early in life, while others appear later. Exposure patterns differ around the world depending on climate, housing, air quality, work conditions, diet, and local plants or insects.
Prevention
Prevention focuses on reducing contact with allergens that cause symptoms. This may include keeping indoor spaces clean and dry, limiting exposure to smoke and air pollution, managing mold, using measures to reduce dust mites, and checking product or food labels carefully. If you know you react to a specific trigger, make a plan with a healthcare professional for how to avoid it.
Diagnosis and Tests
A healthcare professional may ask about symptoms, timing, home or work exposures, foods, medicines, and family history. Testing may include skin tests, blood tests, or supervised exposure testing in selected cases. Do not try to test a possible serious allergy on your own.
Treatment Categories
Treatment depends on the type of allergy, the symptoms, and how severe the reactions are. Main approaches include avoiding triggers, using symptom-relief medicines recommended by a healthcare professional, and in some cases allergy immunotherapy under medical supervision. Severe allergic reactions need urgent emergency treatment.
Living With It
Living with allergies often means learning your triggers and preparing for accidental exposure. Keeping a record of reactions, reading labels, and telling schools, workplaces, or caregivers about important allergies can help. If you have had a serious reaction before, ask a healthcare professional about an emergency action plan.
When to Seek Medical Care
Seek medical care if symptoms are frequent, getting worse, affecting sleep or daily life, or if you are not sure what is triggering them. Also get medical advice after any reaction to a new food, medicine, insect sting, or workplace substance. Children with ongoing allergy symptoms should also be assessed.
When It May Be an Emergency
Get emergency medical help right away for trouble breathing, wheezing that is quickly worsening, swelling of the tongue or throat, fainting, severe dizziness, confusion, or widespread hives with other serious symptoms. A rapid reaction after a food, medicine, or insect sting can be life-threatening. Emergency care is needed even if symptoms seem to improve.