What is an allergic reaction?

An altered reaction. The roots of "allergy" are from greek "allos" (different) and "ergos" (action). So, an allergic reaction is a "different" (from normal) reaction. The reaction occurs to an allergen. An allergen can be a pollen (ragweed), food (peanut), animal (dust mite or bee venom), or other foreign substances. Symptoms occur due to histamine and other chemicals and cause sneezing, runny nose, etc.
A chemical reaction. An allergic reaction is when a trigger, either ingested or in the environment, causes the body to release histamine and leukotrienes. The reaction can be either local, like an insect bite or sting, or systemic (widespread throughout the body) such as what happens with ragweed.
Overreaction. An allergic reaction is an overreaction of the immune system by an allergic individual to a substance that is normally harmless. Reactions can include runny or stuffy nose (allergic rhinitis) wheezing and cough (asthma) or skin reactions like eczema or hive. ( a severe reaction can lead to difficult breathing, shock and even death in the case of anaphylaxis.).

Related Questions

What caused my allergic reaction?

Common question. An allergist is frequently asked to identify the cause of the allergic reaction. Reviewing the symptoms is a good start---cough, wheezing, runny nose, vomiting, diarrhea, rash, itching, eyes puffy, anaphylaxis. There are many triggers of allergic reactions, the most common being pollens, dust, animal dander, foods, medications, insect stings/bites, latex, metals, etc. Finding the cause is key. Read more...

What can an allergic reaction feel like?

Depends where. In the skin itchy. In the nose itchy, sneezy, runny & stuffy. In the eye itchy and teary. In the lungs coughing, wheezing, weight on chest. In the digestive tract nausea, vomiting, cramps, diarrhea. Read more...

Can you tell me what is a allergic reaction?

Allergic reaction. .. is an inappropriate immune response to a trigger, or allergen (eg pollen). The body forms immunity to something it recognizes as foreign, but also "overreacts" to it. Some reactions occur quickly if mediated by antibodies bound to white blood cells called mast cells or basophils (eg peanut allergy) or they occur slowly if mediated by T-cell (eg poison ivy). Less common mechanisms also exist. Read more...

What does an allergic reaction to antibiotics look like?

Depends. It depends on the nature of the immune response. Allergic antibody (IgE) mediated reactions occur rapidly after ingestion and can involve hives, skin swelling, wheezing, shortness of breath, nausea/vomitting, diarrhea, dizziness, confusion, palpitations, loss of consciousness and even death. A delayed reaction can occur after days on the medicine and would have different constellation of symptom. Read more...