What Causes Allergic Reactions?

Allergic reaction to bee sting
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I see patients in my clinic every day who tell me that they’ve had an allergic reaction. However, this term means different things to different people. Most people will say that they experienced a skin rash, such as hives or tongue, lip or throat swelling, as part of their allergic reaction. Others say that their allergic reaction caused them to sneeze and have a runny nose, or have an asthma attack. The most serious form of allergic reactions is anaphylaxis, which involves a "whole body" allergic reaction, not just the skin, and can be life-threatening.

Find out which symptoms tell you that you may have had an allergic reaction.


During an allergic process, the substance responsible for causing the allergy, or allergen, binds to allergic antibodies present on allergic cells in a person's body, including mast cells and basophils. These cells then release chemicals such as histamine and leukotrienes, resulting in allergic symptoms.

The types of symptoms that occur depend on where in the body this reaction takes place. For example, if pollen lands in a person’s nose, then nasal allergies may occur. If the allergen is swallowed, such as with a food allergy, the reaction may result in a whole body reaction, such as hives or anaphylaxis.

Severe Allergic Reactions (Anaphylaxis)

Anaphylaxis is a life-threatening reaction caused by the release of chemicals, such as histamine, leukotrienes, and tryptase, from mast cells. This may result in a variety of symptoms, including low blood pressure (shock), trouble breathing, and skin symptoms such as hives and swelling.

The symptoms of anaphylaxis vary, and may not all be present in a single person experiencing anaphylaxis. Most experts consider anaphylaxis to include symptoms involving the skin and at least one other organ system. Symptoms may include: Skin symptoms, hives, itching or flushing; respiratory symptoms, such as shortness of breath, wheezing and coughing; circulatory symptoms, such as rapid heart rate, lightheadedness and low blood pressure; gastrointestinal symptoms, such as nausea, vomiting, diarrhea and abdominal; nasal symptoms such as sneezing, post-nasal drip and itchy nose and eyes; miscellaneous symptoms, such as menstrual cramps in women, metallic taste and a sense of panic.

Learn more about the causes and diagnosis of anaphylaxis.



Millions of children and adults in the United States suffer from food allergies. When the culprit food is eaten, most allergic reactions occur within minutes. Skin symptoms (such as itching, hives, and swelling) are the most common and occur during most food reactions. Other symptoms can include nasal (sneezing, runny nose, itchy nose, and eyes), gastrointestinal (nausea, vomiting, cramping, diarrhea), respiratory (shortness of breath, wheezing, coughing, chest tightness), and cardiovascular (low blood pressure, light-headedness, rapid heartbeat) symptoms. When severe, this reaction is called anaphylaxis and can be life-threatening.


Fitness to 30% of all hospitalized patients will experience an unintended reaction as a result of medications. However, true allergic reactions to medications only occur in about 1 of 10 of all adverse drug reactions. Skin rashes are the most common symptoms occurring from adverse drug reactions. Hives and swelling suggest an allergic cause, while blistering, peeling and sunburn-like reactions suggest a non-allergic immune system cause (like an autoimmune disease). When a rash blisters and peels, is painful or involves sores in the mouth and mucous membranes, Stevens-Johnson Syndrome or toxic epidermal necrolysis is the likely diagnosis, which can be life-threatening.

Insect Stings and Bites

Nearly everyone has experienced an insect bite or sting at some point in his or her life. Most of the time, these stings and bites lead to mild pain or itching right where they occurred. Sometimes, however, people can experience more severe allergic reactions that could be caused by an allergic reaction to the sting or bite. From bee stings to mosquito bites, and from fire ant stings to bed bug bites, allergic reactions to insects are very common.


For the most part, the treatment of allergic reactions is the same regardless of the cause of the reaction. The initial treatment of anaphylaxis includes the removal of the offending allergen (remove the bee's stinger; stop taking the medication, etc.), as well as the use of various medications, such as injectable epinephrine, antihistamines, and corticosteroids.

Epinephrine is the drug of choice for the initial treatment of anaphylaxis and is available in self-injectable kits for people who are prone to anaphylaxis to carry with them. These people should also consider wearing a Medic-Alert bracelet so that medical personnel can quickly identify their condition in an emergency.

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