9 Common Allergies Explained

A woman sneezing into her hand

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About one out of every five Americans suffer from allergies, which are simply exaggerated immune responses to harmless substances. The immune system typically protects the body from viruses and bacteria, but a person with allergies has an overly sensitive system that releases chemicals such as histamines — which can cause symptoms like itching, swelling, and hives.

Here’s a look at some of the most common types of allergies — from milk to pet dander — and how to cope with them.

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Wheat and foods made with it are staples of the American diet, but some people's immune systems develop antibodies to certain wheat proteins, causing a wheat allergy. An allergic reaction to wheat can cause a variety of symptoms, including nausea, hives and difficulty breathing, and such an allergy can also cause anaphylaxis, a deadly reaction that causes swelling of the throat and airways.

The best treatment for a wheat allergy is simply to avoid consuming foods that contain it. People with this allergy must check ingredient labels before eating anything because many processed foods, including ice cream and ketchup, contain wheat flour.

Wheat allergies are different from celiac disease, which causes intestinal inflammation when a person eats a food that contains gluten, a type of wheat protein.

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Penicillin is one of the most commonly prescribed antibiotics used to treat bacterial infections, and it's also one of the most common drug allergies. A penicillin allergy is an overreaction by your immune system to penicillin and related antibiotics.

Allergic reactions to penicillin can range from a rash to life-threatening anaphylaxis, which typically develops within an hour of taking the drug. Doctors aren't sure why some people develop a penicillin allergy, but once someone has had a reaction to it, the easiest way to prevent another reaction is to avoid penicillin and related antibiotics.

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Egg allergies are one of the most common food allergies, especially among children. However, most children outgrow their egg allergy by the age of 5. Most people who are allergic to eggs have reactions to the proteins in egg whites, but some people can't tolerate the proteins in the yolk.

An allergic reaction to eggs typically occurs within a few minutes to a few hours after eating eggs or foods that contain them. Symptoms are usually mild, such as rashes, hives and vomiting, but a severe egg allergy can cause anaphylaxis. If allergies are mild, people may be able to relieve symptoms with over-the-counter antihistamine medications, but people who are especially sensitive to eggs must keep them out of the house because egg fumes or even getting eggs on the skin can cause severe allergic reactions.

A variety of food products contain eggs, making avoidance more complicated.

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Cats and dogs


About half of U.S. households have a cat or a dog, and an estimated 10 percent of the population may be allergic to these animals. Allergens from cats and dogs are found in skin cells the animals shed — which is known as dander — and in saliva and on hairs.

Dander is particularly problematic because it's small and can remain airborne for long periods of time, and because it easily accumulates on clothing, curtains and upholstered furniture. Pet saliva can collect in carpets, bedding, furniture and clothing, and dried saliva can also become airborne.

Like other allergies, reactions to cats and dogs can range from mild to severe. Some people receive allergy shots to cope with exposure, and some can simply take over-the-counter antihistamines to relieve symptoms. So-called hypoallergenic cats and dogs may shed less than other pets; however, no breeds are truly hypoallergenic.

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We're all exposed to some mold on a daily basis with no negative effect; however, people with mold allergies may have a reaction if exposed to too much of the fungus. If you have a mold allergy, your immune system overreacts to mold spores, causing wheezing, a stuffy or runny nose, itchy eyes and rashes or hives. An allergy to mold can also exacerbate asthma symptoms, severely restricting breathing.

If you're allergic to mold, the best defense is to reduce your exposure to it, and certain medications can also help keep allergic reactions under control.

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Milk allergy is one of the most common food allergies in children, but most children outgrow it by the age of 3. Although proteins in cow's milk are the usual cause of such an allergy, milk from goats, sheep and buffalo can also cause an allergic reaction.

Avoidance is the best treatment for milk allergy, but so many foods contain milk or milk products these days that people with the allergy have to pay close attention to just about everything they eat. An allergic reaction to milk typically occurs a few minutes to a few hours after consuming milk, and symptoms can include wheezing, vomiting, hives and digestive problems. Rarely, milk allergy can cause anaphylaxis.

A milk allergy is not the same as lactose intolerance — it's an allergy that involves the immune system whereas lactose intolerance involves the digestive system. People who are lactose intolerant don't produce enough of the enzyme to break down the sugar in milk.

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Todd Sumlin, The Charlotte Observer/AP.

Pollen is composed of the microscopic cells of flowering plants, and it spreads through the air during the spring, summer and fall to fertilize plants and tree flowers. Pollen can be easily inhaled during these seasons, causing symptoms such as sneezing, nasal congestion, watery eyes, runny nose and itchy throat. Pollen allergies can trigger or worsen asthma and lead to sinus or ear infections.

If you have pollen allergies, pay attention to what time of year your symptoms occur and try to lessen your exposure to the substance during that time. Keep your windows and doors closed as much as possible. If you have to be outdoors, wear sunglasses to minimize pollen in your eyes, and remove your clothing when you come indoors and take a shower. Don't garden, rake leaves or mow your lawn if possible, and when landscaping, choose trees that don't produce a lot of pollen such as crape myrtles, dogwoods and palms. If efforts to avoid pollen aren't effective, your doctor may suggest you take decongestants or antihistamines, use a nasal spray or receive allergy shots.

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A peanut allergy is a reaction that occurs when your body mistakenly identifies peanuts as harmful substances, causing your immune system to release chemicals, including histamine, into your blood. The allergy is fairly common; it's one of the most common causes of severe allergy attacks, and even tiny amounts of peanuts or products that contain them can cause a serious reaction.

A mild reaction may result in a runny nose, skin rash, stomachache or tingling on the lips or tongue, but reactions can worsen, causing throat tightening, wheezing, vomiting and diarrhea. People who are allergic to peanuts can also suffer from a life-threatening reaction called anaphylaxis, which can cause difficulty breathing, a dangerous drop in blood pressure and death. Anaphylaxis usually happens within minutes but can occur after several hours of consuming peanuts.

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Photo: By Davdeka/Shutterstock

Allergic reactions to sunlight occur when ultraviolet radiation triggers changes in your skin cells. These changes cause your immune system to mistake proteins in your skin for harmful substances, causing allergy symptoms. Most people with sun allergies suffer symptoms only when exposed to bright sunlight during spring and summer months; however, people with severe sun allergies can have reactions even during winter months.

An allergic reaction to UV rays can cause a variety of symptoms, including rashes, swollen skin, hives, blisters and itchy skin. It isn't clear why some people have a sun allergy, but doctors think genetics may play a role. Sun allergies can be treated using oral antihistamines, topical steroid creams and UV therapy, but the best way to prevent a reaction is to avoid exposure to the sun.

Certain medications, medical conditions or chemicals in hair or skin products can cause increased photosensitivity, but this isn't a true allergic reaction to the sun.