- An allergic reaction is the body’s way of responding to an “invader.” When the body senses a foreign substance called an antigen, the immune system is activated. The immune system normally protects the body from harmful substances such as bacteria and toxins. The exaggerated reaction to a harmless substance (an allergen) is called a hypersensitivity reaction or an allergic reaction.
- Anything can be an allergen. Dust, pollen, plants, medicines (such as ibuprofen, sulfa drugs such as sulfamethoxazole and trimethoprim (Bactrim), codeine, amoxicillin (Amoxil, Amoxil Pediatric Drops, Trimox), cephalexin (Keflex)), foods (common food allergies include shrimp and other shellfish, peanuts ), insect bites (such as mosquito bites or bee stings), animal dander (such as from a pet cat or dog, or rodents), viruses or bacteria are examples of allergens.
- Reactions can occur in one place, such as a small localized rash, itchy eyes, bumps on the face, or anywhere, such as a whole body rash such as hives (urticaria).
- Most allergic reactions are minor, such as rash from poison ivy, mosquito or other insect bites, or sneezing from hay fever. The type of response depends on the response of the individual’s immune system, which is sometimes unpredictable.
- In rare cases, an allergic reaction can be life-threatening (known as anaphylaxis). The Asthma and Allergy Base of America (AAFA) estimates that at least one in 50 Americans (1.6%) and as many as one in 20 (5.1%) have had anaphylaxis, resulting in an average of 63-99 deaths per year.
- Allergies are very common. AAFA states that allergies affect 50 million Americans, are the second-largest chronic disease in the U.S. and the third-largest chronic disease in children under age 18. More than 40 million people have indoor and outdoor allergies as a primary allergy. In 2012, more than 11 million people in the U.S. visited their doctor for allergic rhinitis, and food allergies account for 200,000 emergency room visits and 10,000 hospitalizations per year.
What causes an allergic reaction?
Almost anything can cause an allergic reaction.
- The body’s immune system includes the white blood cells that produce antibodies.
- When the body is exposed to an antigen (a foreign body such as pollen that can cause an immune reaction), a complex set of reactions starts.
- The white blood cells produce an antibody specific for that antigen. This is called ‘sensitization’.
- The antibodies work to help white blood cells detect and destroy substances that cause disease and illness. In allergic reactions, the antibody belongs to the class of immunoglobulins known as immunoglobulin E or IgE.
- This antibody type promotes the production and release of chemicals and hormones called ‘mediators’.
- Mediators have effects on local tissue and organs in addition to activating more white blood cell defenders. It is these effects that cause the symptoms of the reaction.
- Histamine is one of the better known allergy products produced by the body.
- If the delivery of the mediators is sudden or extensive, the allergic reaction can also be sudden and severe, and anaphylaxis can occur.
- Allergic reactions are unique to each person. The reaction time for allergens can vary greatly. Some people will have an allergic reaction immediately; for others, it can take hours to days to develop.
- Most people are aware of their specific triggers and reactions to allergies.
- There are more than 160 allergenic foods. Certain foods are common allergens, including peanuts, strawberries, shellfish, shrimp, dairy, and wheat.
- Babies can also have food allergies. Common foods that can cause allergic reactions in babies are milk, eggs, nuts and soy. People should talk to their child’s pediatrician if they are concerned about food allergies in their baby.
- Food intolerance is not the same as food allergies. Allergies are a reaction of the immune system, while food intolerance is a reaction of the digestive system in which a person is unable to properly digest or break down a certain food.
- People can be allergic to wheat, but not gluten. According to the American College of Allergy, Asthma & Immunology, there is no such thing as a gluten allergy; but one may have a sensitivity to this protein that results in gastrointestinal symptoms.
- Certain fruits or vegetables can cause an itchy mouth or scratchy throat after eating in people with oral allergy syndrome.
- Seasonal allergic rhinitis (also known as hay fever) is an allergy that occurs in the spring, summer, or early fall caused by allergies to pollen from trees, grasses, or weeds, or to mold.
- Vaccines and medicines (antibiotics such as penicillin and amoxicillin, aspirin, ibuprofen, iodine), general anesthesia and local anesthetics, latex rubber (such as in gloves or condoms), dust, mold or other fungi, animal dander from pets and other animals, and Poison Ivy are known allergens. Other known allergens can include detergents, hair dyes, cosmetics and the ink in tattoos.
- Bee stings, stingers, penicillin and peanuts are known to cause dramatic reactions that can be serious and involve the entire body.
- Minor injuries, hot or cold temperatures, exertion, stress or emotions can cause allergic reactions.
- Sun exposure can cause allergic reactions in some people, often referred to as “sun poisoning.”
- Often the specific allergen cannot be identified unless someone has had a similar reaction in the past.
- Allergies, and the tendency to have allergic reactions, are hereditary – that is, it occurs in some families.
- Many people with one trigger usually have other triggers as well.
- Risk factors for allergic reactions include certain medical conditions that can make a person more likely to have allergic reactions:
- Severe allergic reaction in the past
- Asthma
- Lung conditions that affect breathing, such as chronic obstructive pulmonary disease (COPD)
- Nasal polyps
- Frequent infections of the paranasal sinuses, ears or airways
- Sensitive skin, especially people with eczema
What are symptoms and signs of an allergic reaction?
The appearance of an allergic reaction depends on the body part and the severity of the reaction. Some responses may be localized and limited, while others may involve multiple body systems. Reactions to the same allergen vary from person to person.
- Anaphylaxis is the term for any combination of allergic symptoms that is fast or sudden and potentially life-threatening. Call 9-1-1 or get immediate medical attention for suspected anaphylaxis.
- A sign of anaphylaxis is shock. Shock has a very specific meaning in medicine. Shock can quickly lead to death. The body’s organs are not getting enough blood because of dangerously low blood pressure. The person in shock may be pale or red, sweaty or dry, confused, anxious, or unconscious.
- Breathing can be difficult or noisy, or the person may not be able to breathe.
- Shock is caused by sudden widening of the blood vessels. This is caused by the action of the mediators. If the drop in blood pressure is sudden and drastic, it can lead to unconsciousness, even cardiac arrest and death.
- Symptoms and signs of an allergic reaction include all, some or many of the following:
- Skin: irritation, redness, itching, swelling, blistering, weeping, crusting, rash, eruptions, or hives (itchy bumps or welts)
- Lungs: wheezing, tightness, coughing, or shortness of breath
- Head: swelling or bumps on the face and neck, eyelids, lips, tongue or throat, hoarseness of voice, headache
- Nose: stuffy nose, runny nose (clear, thin discharge), sneezing, postnasal drip
- Eyes: red (bloodshot), itchy, swollen, or watery, or swelling of the area around the face and eyes
- Stomach: pain, nausea, vomiting, diarrhea or bloody diarrhea
- Other: feeling tired or tired, sore throat, dizziness or lightheadedness
When should someone seek medical care for an allergic reaction?
Because allergic reactions can progress and worsen within minutes, causing complications, medical attention is always recommended for all but the most insignificant and localized symptoms.
If the symptoms of an allergic reaction worsen over a few days, or if they do not improve with the recommended treatment and removal of the allergen, contact a doctor.
People should tell a doctor if they have allergic symptoms after taking a prescription drug or other prescribed treatment (see Drug Allergy).
Allergic reactions can be dangerous. Sudden, severe and widespread reactions require an emergency evaluation by a physician. Call 9-1-1 or call emergency medical services if someone has any of the following with an allergic reaction:
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- Sudden, severe or rapidly worsening symptoms
- Exposure to an allergen that previously caused serious or bad reactions
- Swelling of the face, lips, tongue or throat
- Wheezing, chest tightness, loud breathing, trouble breathing or hoarseness of voice
- Confusion, sweating, nausea, or vomiting
- Widespread rash or severe hives
- Dizziness, collapse or unconsciousness
What tests do healthcare professionals use to diagnose an allergic reaction?
For typical allergic reactions, a doctor will examine a person and ask questions about his or her symptoms and their timing. Blood tests and X-rays are not necessary except in unusual circumstances.
In case of severe reactions, an individual will be quickly evaluated in an emergency department to make a diagnosis. The first step for the doctor is to assess the severity of the allergic reaction.
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- Blood pressure and heart rate are monitored.
- An examination determines whether the patient needs help breathing.
- Often an intravenous line is placed in the event that anti-allergy (antihistamines) medications are needed quickly.
- If the patient is able to speak, he or she will be asked about allergy triggers and previous reactions.
