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Peanut allergy affects approximately 1.5 million people in the United States. As the most common cause of life-threatening allergic reactions (anaphylaxis), peanut allergies account for 80 percent of fatal or near-fatal allergic reactions each year. You can reduce your risk of having an allergic reaction to peanuts by knowing as much as you can about peanut allergy and how to avoid peanut-containing products.

If you have any reaction to peanuts, tell your doctor about it, no matter how mild the reaction may have been. Tests can help diagnose peanut allergy, so you can take steps to avoid future and potentially worse reactions.

There's a difference between peanut allergy and peanut intolerance. Sometimes it can be difficult to know whether you are allergic or intolerant to peanuts.

• Peanut intolerance. If you have peanut intolerance, you usually can eat small amounts of peanuts with only mild symptoms, such as indigestion or heartburn, or no reaction at all. A peanut intolerance doesn't involve your immune system.
• Peanut allergy. An allergy to peanuts involves an immune system response. Even a tiny amount of peanuts may trigger a serious allergic reaction. Tests can help determine whether you have true peanut allergy.

Peanut allergies trigger an immune system response. Your immune system reacts to proteins found in peanuts. Exposure to peanuts or traces of peanuts may cause immediate reactions, such as itching, redness, swelling, shortness of breath, wheezing, nausea, abdominal pain, lightheadedness or loss of consciousness (anaphylaxis).The chemicals in peanuts can cause hives to develop on the areas of your skin that have come in contact with peanuts or traces of peanuts. Hives may spread to the rest of your body.

Allergic reactions to peanuts usually occur within minutes after exposure, although reactions within an hour or so after ingestion are possible. Signs and symptoms can range in severity depending on which body systems are involved in a reaction and how much peanut protein you've been exposed to.

The most serious and potentially deadly allergic reaction to peanuts is an anaphylactic response. If you are highly sensitive, an anaphylactic reaction can develop immediately after peanut exposure, causing the airways (bronchi) to constrict, making breathing difficult. Blood pressure may drop to life-threateningly low levels, making you feel dizzy or lose consciousness. Other serious signs and symptoms of an anaphylactic reaction include:

• Wheezing
• Rapid or weak pulse
• Blueness of your skin, including your lips and nail beds
• Diarrhea
• Nausea and vomiting
• Dizziness
• Loss of consciousness

Seek emergency medical care if you or someone else develops an anaphylactic reaction.

Peanut allergy is caused by an immune system malfunction. Your immune system identifies peanuts as harmful triggering the production of immunoglobulin E (IgE) antibodies to neutralize the peanut protein (allergen). The next time you come in contact with peanuts, these IgE antibodies recognize it and signal your immune system to release histamine and other chemicals into your bloodstream.

Histamine and other body chemicals cause a range of allergic signs and symptoms. Histamine is partly responsible for most allergic responses, including runny nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, labored breathing and even anaphylactic shock.

Exposure to peanuts can occur in three ways:

• Direct contact. The most common cause of peanut allergy is direct contact with peanuts. This means exposure via all routes of contact — usually through eating peanuts, but including kissing or touching someone who's been in direct contact with peanuts.
• Cross-contact. This is the unintended introduction of peanuts into a product. It's generally the result of exposure to peanuts during processing or handling of a food product.
• Inhalation. An allergic reaction may occur if you inhale dust or aerosols containing peanuts, such as that of peanut flour or peanut oil cooking spray.

Common food products that can trigger peanut allergy symptoms if they contain peanut proteins include:

• Peanut butter
• Peanut flour
• Ground or mixed nuts
• Baked goods, such as cookies and pastries
• Ice cream and frozen desserts
• Energy bars
• Salad dressing
• Cereals and granola
• Grain breads
• Marzipan (a molding confection made of nuts, egg whites and sugar)
• Nougat

Peanuts may be present in not-so-obvious foods including:

• Arachis oil. This is another name for peanut oil. Pure peanut oil usually doesn't trigger allergic reactions because peanut proteins are usually removed during processing. However, peanut oil can become contaminated with peanut proteins.
• Artificial tree nuts. Peanuts can be flavored to taste like other nuts, such as walnuts or pecans.
• Chocolate candies. Some chocolate candies are produced on equipment that is also used for processing peanuts or peanut-containing foods.
• Cultural foods. Some African, Chinese, Indonesian, Mexican, Thai and Vietnamese dishes often contain peanuts or are exposed to peanuts during restaurant preparation.
• Nut butters. Nut butters, such as cashew nut butter, are often processed by the same equipment used to make peanut butter.
• Specialty items. Foods sold in bakeries and ice-cream shops may come in contact with peanuts.
• Sunflower seeds. Many brands of sunflower seeds are processed on equipment also used to produce peanuts.

It isn't clear why some people develop allergies while others don't. However, people with certain risk factors have a greater chance of developing peanut allergy:

• Family history of allergies. You're at increased risk of peanut allergy if other allergies, especially other types of food allergies, are common in your family. A child's first allergic reaction to peanuts usually occurs between ages 1 and 2.
• Personal history of peanut allergy. About 20 percent to 25 percent of children with peanut allergy outgrow it. However, even if you seem to have outgrown peanut allergy, there is still a small risk it will recur.
• Altered immune system. According to recent studies, the prevalence of peanut allergy has doubled in young American children in the last five years. Although reasons are unknown, some scientists believe that the destroying of many infectious diseases may have altered the immune system. Other experts suggest that improved hygiene is involved, proposing that higher standards of cleanliness in Western countries may have confused our immune systems, increasing the chances of developing allergies later in life, when the immune system is usually more prepared to prevent allergies from occurring.

Talk to your doctor if you think you're allergic to peanuts or if you have peanut allergy symptoms. If possible, see your doctor while you have symptoms. Seek emergency medical treatment if you develop any signs or symptoms of anaphylaxis.

Your doctor will want to know your signs and symptoms and may want to conduct a physical examination to identify or exclude other medical problems. He or she may also recommend one or both of the following tests:

• Skin test. In this test, your skin is pricked and exposed to small amounts of the proteins found in peanuts to see if you have a skin test response. If you're allergic, you develop a raised bump (hive) at the test location on your skin. Allergy specialists usually are best equipped to perform allergy skin tests.
• Blood test. A blood test can measure your immune system's response to peanuts by measuring the amount of certain antibodies in your bloodstream, known as immunoglobulin E (IgE) antibodies. A blood sample is sent to a medical laboratory, where it can be tested for evidence of sensitivity to peanuts.

Medications, such as antihistamines, may reduce symptoms of peanut allergies. These drugs can be taken after exposure to peanuts to control your reaction and help relieve discomfort. However, the only way to prevent an allergic reaction is to avoid peanuts and peanut proteins altogether.

Despite your best efforts, you may still come into contact with peanuts and have a severe reaction. In this case, you may need an emergency injection of adrenaline (epinephrine) and a trip to the emergency room. If you're at risk of having a severe reaction, you may need to carry injectable epinephrine with you at all times.

The best way to prevent an allergic reaction to peanuts is to know and avoid foods that cause signs and symptoms. In some foods, peanuts may be well hidden. This is especially true in restaurants and in other social settings.

If you know you have peanut allergy, follow these steps:

• Know what you're eating and drinking. Be sure to read food labels carefully.
• If you've already had a severe reaction to peanuts, wear a medical alert bracelet or necklace.
• Talk with your doctor about carrying emergency medications.

If your child has peanut allergy, take these precautions to ensure his or her safety:

• Notify key people that your child has peanut allergy. Talk with child care providers, school personnel, parents of your child's friends, and other adults who regularly interact with your child. Emphasize that an allergic reaction can be life-threatening and requires immediate action. Make sure that your child also knows to ask for help right away if he or she reacts to peanuts.
• Explain peanut allergy symptoms. Teach the adults who spend time with your child how to recognize signs and symptoms of an allergic reaction to peanuts.
• Write an action plan. Your plan should describe how to care for your child when he or she has an allergic reaction to peanuts. Provide a copy of the plan to your child's school and to others who care for and supervise your child.
• Have your child wear a medical alert bracelet or necklace. This alert lists your child's allergy symptoms and explains how others can provide first aid in an emergency.
• Discourage your child from sharing foods. It's common for kids to share snacks and treats. However, during times of fun your child may forget about food allergies or sensitivities. If your child is allergic to peanuts, encourage him or her to refrain from eating food from others.