What Are Allergies? Allergies are abnormal immune system reactions to things that are typically harmless to most people. When a person is allergic to something, the immune system mistakenly believes that this substance is harming the body. Substances that cause allergic reactions — such as some foods, dust, plant pollen, or medicines — are known as allergens. Allergies are a major cause of illness in the United States. Up to 50 million Americans, including millions of kids, have some type of allergy. In fact, allergies cause about 2 million missed school days each year. How Do Allergies Happen? An allergy happens when the immune system& overreacts to an allergen, treating it as an invader and trying to fight it off. This causes symptoms that can range from annoying to serious or even life-threatening. In an attempt to protect the body, the immune system makes antibodies called immunoglobulin E (IgE). These antibodies then cause certain cells to release chemicals (including histamine) into the bloodstream to defend against the allergen "invader." It's the release of these chemicals that causes allergic reactions. Reactions can affect the eyes, nose, throat, lungs, skin, and gastrointestinal tract. Future exposure to that same allergen will trigger this allergic response again. Some allergies are seasonal and happen only at certain times of the year (like when pollen counts are high); others can happen anytime someone comes in contact with an allergen. So, when a person with a food allergy eats that particular food or someone who's allergic to dust mites is exposed to them, they will have an allergic reaction. Who Gets Allergies? The tendency to develop allergies is often hereditary, which means it can be passed down through genes from parents to their kids. But just because you, your partner, or one of your children might have allergies doesn't mean that all of your kids will definitely get them. And someone usually doesn't inherit a particular allergy, just the likelihood of having allergies. Some kids have allergies even if no family member is allergic, and those who are allergic to one thing are likely to be allergic to others. What Things Cause Allergies? Common Airborne Allergens Some of the most common things people are allergic to are airborne (carried through the air): Dust mites are microscopic insects that live all around us and feed on the millions of dead skin cells that fall off our bodies every day. They're the main allergic component of house dust. Dust mites are present year-round in most parts of the United States and live in bedding, upholstery, and carpets. Pollen is a major cause of allergies (a pollen allergy is often called hay fever or rose fever). Trees, weeds, and grasses release these tiny particles into the air to fertilize other plants. Pollen allergies are seasonal, and the type of pollen someone is allergic to determines when symptoms happen. Pollen counts measure how much pollen is in the air and can help people with allergies predict how bad their symptoms might be on any given day. Pollen counts are usually higher in the morning and on warm, dry, breezy days, and lowest when it's chilly and wet. Molds are fungi that thrive both indoors and outside in warm, moist environments. Outdoors, molds can be found in poor drainage areas, such as in piles of rotting leaves or compost piles. Indoors, molds thrive in dark, poorly ventilated places such as bathrooms and damp basements. Molds tend to be seasonal, but some can grow year-round, especially those indoors. Pet allergens are caused by pet dander (tiny flakes of shed skin) and animal saliva. When pets lick themselves, the saliva gets on their fur or feathers. As the saliva dries, protein particles become airborne and work their way into fabrics in the home. Pet urine also can cause allergies in the same way when it gets on airborne fur or skin, or when a pet pees in a spot that isn't cleaned. Cockroaches are also a major household allergen, especially in inner cities. Exposure to cockroach-infested buildings may be a major cause of the high rates of asthma in inner-city kids. Common Food Allergens Up to 2 million, or 8%, of kids in the United States are affected by food allergies. Eight foods account for most of those: cow's milk, eggs, fish and shellfish, peanuts and tree nuts, soy, and wheat. Cow's milk (or cow's milk protein). Between 2% and 3% of children younger than 3 years old are allergic to the proteins found in cow's milk and cow's milk-based formulas. Most formulas are cow's milk-based. Milk proteins also can be a hidden ingredient in prepared foods. Many kids outgrow milk allergies. Eggs. Egg allergy can be a challenge for parents. Eggs are used in many of the foods kids eat — and in many cases they're "hidden" ingredients. Kids tend to outgrow egg allergies as they get older. Fish and shellfish. These allergies are some of the more common adult food allergies and ones that people usually don't outgrow. Fish and shellfish are from different families of food, so having an allergy to one does not necessarily mean someone will be allergic to the other. Peanuts and tree nuts. Peanut allergies are on the rise, and as are allergies to tree nuts, such as almonds, walnuts, pecans, hazelnuts, and cashews. Most people do not outgrow peanut or tree nut allergies. Soy. Soy allergy is more common among babies than older kids. Many infants who are allergic to cow's milk are also allergic to the protein in soy formulas. Soy proteins are often a hidden ingredient in prepared foods. Wheat. Wheat proteins are found in many foods, and some are more obvious than others. Although wheat allergy is often confused with celiac disease, there is a difference. Celiac disease is a sensitivity to gluten (found in wheat, rye, and barley). But a wheat allergy can do more than make a person feel ill — like other food allergies, it also can cause a life-threatening reaction. Other Common Allergens Insect allergy. For most kids, being stung by an insect means swelling, redness, and itching at the site of the bite. But for those with insect venom allergy, an insect sting can cause more serious symptoms. Medicines. Antibiotics are the most common type of medicines that cause allergic reactions. Many other others, including over-the-counter medicines (those you can buy without a prescription), also can cause allergic reactions. Chemicals. Some cosmetics or laundry detergents can make people break out in hives. Usually, this is because someone has a reaction to the chemicals in these products, though it may not always be an allergic reaction. Dyes, household cleaners, and pesticides used on lawns or plants also can cause allergic reactions in some people. Some kids also have what are called cross-reactions. For example, kids who are allergic to birch pollen might have symptoms when they eat an apple because that apple is made up of a protein similar to one in the pollen. And for reasons that aren't clear, people with a latex allergy (found in latex gloves and some kinds of hospital equipment) are more likely to be allergic to foods like kiwi, chestnuts, avocados, and bananas. What Are the Signs and Symptoms of Allergies? The type and severity of allergy symptoms vary from allergy to allergy and person to person. Allergies may show up as itchy eyes, sneezing, a stuffy nose, throat tightness, trouble breathing, vomiting, and even fainting or passing out. Kids with severe allergies (such as those to food, medicine, or insect venom) can be at risk for a sudden, potentially life-threatening allergic reaction called anaphylaxis. Anaphylaxis can happen just seconds after being exposed to an allergen or not until a few hours later (if the reaction is from a food). So doctors will want anyone diagnosed with a life-threatening allergy to carry an epinephrine auto-injector in case of an emergency. Epinephrine works quickly against serious allergy symptoms; for example, it reduces swelling and raises low blood pressure. Airborne Allergy Symptoms Airborne allergens can cause something known as allergic rhinitis, which usually develops by 10 years of age, reaches its peak in the teens or early twenties, and often disappears between the ages of 40 and 60. Symptoms can include: sneezing itchy nose and/or throat stuffy nose coughing When symptoms also include itchy, watery, and/or red eyes, this is called allergic conjunctivitis. (Dark circles that sometimes show up around the eyes are called allergic "shiners.") Food, Medicines, or Insect Allergy Symptoms wheezing trouble breathing coughing hoarseness throat tightness stomachache vomiting diarrhea itchy, watery, or swollen eyes hives swelling a drop in blood pressure, causing lightheadedness or loss of consciousness Allergic reactions can vary. Sometimes, a person can have a mild reaction that affects only one body system, like hives on the skin. Other times, the reaction can be more serious and involve more than one part of the body. A mild reaction in the past does not mean that future reactions will be mild. How Are Allergies Diagnosed? Some allergies are fairly easy to identify but others are less obvious because they can be similar to other conditions. If your child has cold-like symptoms lasting longer than a week or two or develops a "cold" at the same time every year, talk with your doctor, who might diagnose an allergy and prescribe medicines, or may refer you to an allergist (a doctor who is an expert in the treatment of allergies) for allergy tests. To find the cause of an allergy, allergists usually do skin tests for the most common environmental and food allergens. A skin test can work in one of two ways: A drop of a purified liquid form of the allergen is dropped onto the skin and the area is scratched with a small pricking device. A small amount of allergen is injected just under the skin. This test stings a little but isn't painful. After about 15 minutes, if a lump surrounded by a reddish area (like a mosquito bite) appears at the site, the test is positive. Blood tests may be done instead for kids with skin conditions, those who are on certain medicines, or those who are very sensitive to a particular allergen. Even if testing shows an allergy, a child also must have symptoms to be diagnosed with an allergy. For example, a toddler who has a positive test for dust mites and sneezes a lot while playing on the floor would be considered allergic to dust mites. How Are Allergies Treated? There's no cure for allergies, but symptoms can be managed. The best way to cope with them is to avoid the allergens. That means that parents must educate their kids early and often, not only about the allergy itself, but also about the reactions they can have if they consume or come into contact with the allergen. Telling all caregivers (childcare staff, teachers, family members, parents of your child's friends, etc.) about your child's allergy is also important. If avoiding environmental allergens isn't possible or doesn't help, doctors might prescribe medicines, including antihistamines, eye drops, and nasal sprays. (Many of these also are available without a prescription.) In some cases, doctors recommend allergy shots (immunotherapy) to help desensitize a person to an allergen. But allergy shots are only helpful for allergens such as dust, mold, pollens, animals, and insect stings. They're not used for food allergies. Airborne Allergies To help kids avoid airborne allergens: Keep family pets out of your child's bedroom. Remove carpets or rugs from your child's room (hard floors don't collect dust as much as carpets do). Don't hang heavy drapes and get rid of other items that allow dust to build up. Clean when your child is not in the room. Use special covers to seal pillows and mattresses if your child is allergic to dust mites. If your child has a pollen allergy, keep the windows closed when pollen season is at its peak, have your child take a bath or shower and change clothes after being outdoors, and don't let him or her mow the lawn. Keep kids who are allergic to mold away from damp areas, such as some basements, and keep bathrooms and other mold-prone areas clean and dry. Food Allergies Kids with food allergies must completely avoid products made with their allergens. This can be tough as allergens are found in many unexpected foods and products. Always read labels to see if a packaged food contains your child's allergen. Manufacturers of foods sold in the United States must state in understandable language whether foods contain any of the top eight most common allergens. This label requirement makes things a little easier. But it's important to remember that "safe" foods could become unsafe if food companies change ingredients, processes, or production locations. Cross-contamination means that the allergen is not one of the ingredients in a product, but might have come into contact with it during production or packaging. Companies are not required to label for cross-contamination risk, though some voluntarily do so. You may see statements such as "May contain…," "Processed in a facility that also processes…," or "Manufactured on equipment also used for …." Because products without such statements also might be cross-contaminated and the company did not label for it, it's always best to contact the company to see if the product could contain your child's allergen. Look for this information on the company's website or email a company representative. Cross-contamination also can happen at home or in restaurants when kitchen surfaces or utensils are used for different foods. Back to Articles Related Articles Allergies Explore more than 20 articles in English and Spanish about all aspects of allergies in children. Read More Serious Allergic Reactions (Anaphylaxis) Kids with severe allergies can be at risk for a sudden, serious allergic reaction called anaphylaxis. 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