Allergic disease is one of the most common chronic health conditions in the world. People with a family history of allergies have an increase risk of developing allergic disease. Hay fever (allergic rhinitis), eczema, hives, asthma, and food allergy are some types of allergic diseases. Allergy symptoms can range from mild to a serious, life-threatening allergic reaction (anaphylaxis).
Allergic reactions begin in your immune system. When a harmless substance such as dust, mold, or pollen is encountered by a person who is allergic to that substance, the immune system may over react by producing antibodies that "attack" the allergen. The can cause wheezing, itching, runny nose, watery or itchy eyes, and other symptoms.
What is the immune system?
The purpose of the immune system is to defend itself and keep microorganisms, such as certain bacteria, viruses, and fungi, out of the body, and to destroy any infectious microorganisms that do invade the body. The immune system is made up of a complex and vital network of cells and organs that protect the body from infection.
The organs involved with the immune system are called the lymphoid organs. They affect growth, development, and the release of lymphocytes (a type of white blood cell). The blood vessels and lymphatic vessels are important parts of the lymphoid organs. They carry the lymphocytes to and from different areas in the body. Each lymphoid organ plays a role in the production and activation of lymphocytes.
Lymphoid organs include:
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Adenoids (two glands located at the back of the nasal passages)
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Appendix (a small tube that is connected to the large intestine)
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Blood vessels (the arteries, veins, and capillaries through which blood flows)
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Bone marrow (the soft, fatty tissue found in bone cavities)
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Lymph nodes (small organs shaped like beans, which are located throughout the body and connect via the lymphatic vessels)
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Lymphatic vessels (a network of channels throughout the body that carries lymphocytes to the lymphoid organs and bloodstream)
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Peyer's patches (lymphoid tissue in the small intestine)
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Spleen (a fist-sized organ located in the abdominal cavity)
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Thymus (two lobes that join in front of the trachea behind the breast bone)
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Tonsils (two oval masses in the back of the throat)
How does a person become allergic?
Allergens can be inhaled, ingested, or enter through the skin. Common allergic reactions, such as hay fever, certain types of asthma, and hives are linked to an antibody produced by the body called immunoglobulin E (IgE). Each IgE antibody can be very specific, reacting against certain pollens and other allergens. In other words, a person can be allergic to one type of pollen, but not another. When a susceptible person is exposed to an allergen, the body starts producing a large quantity of similar IgE antibodies. The next exposure to the same allergen may result in an allergic reaction. Symptoms of an allergic reaction will vary depending on the type and amount of allergen encountered and the manner in which the body's immune system reacts to that allergen.
Allergies can affect anyone, regardless of age, gender, race, or socioeconomic status. Generally, allergies are more common in children. However, a first-time occurrence can happen at any age, or recur after many years of remission. Hormones, stress, smoke, perfume, or environmental irritants may also play a role in the development or severity of allergies.
What is anaphylactic shock?
Anaphylactic shock, also called anaphylaxis, is a severe, life-threatening reaction to certain allergens. Body tissues may swell, including tissues in the throat. Anaphylactic shock is also characterized by a sudden drop in blood pressure. The following are the most common symptoms of anaphylactic shock. However, each person may experience symptoms differently. Other symptoms may include:
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Itching and hives over most of the body
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Feeling warm
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Swelling of the throat and tongue or tightness in throat
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Difficulty breathing or shortness of breath
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Dizziness
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Headache
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Pain or cramps
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Nausea, vomiting, or diarrhea
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Shock
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Loss of consciousness
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Feeling light-headed
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Anxiety
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Abnormal heart rate (too fast or too slow)
Anaphylactic shock can be caused by an allergic reaction to a drug, food, serum, insect venom, allergen extract, or chemical. Some people who are aware of their allergic reactions or allergens carry an emergency anaphylaxis kit that contains injectable epinephrine (a drug that stimulates the adrenal glands and increases the rate and force of the heartbeat).
For information about food allergies please visit the following pages:
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Food allergy
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Food allergies in children
Medically Reviewed by Nayana Ambardekar, MD on June 13, 2020
Will your allergy symptoms get better or even go away? Or are they “chronic,” which means they are here for the long run? The answer isn’t always simple. Each person's case is different. Some people, most often children, may outgrow an allergy completely. Others find that with age, their allergy symptoms lighten up. That may be because the immune system can weaken with age, and perhaps can't muster as strong a reaction to the allergen. But as an adult, once you have an allergy, it usually doesn't go away on its own. Some people find that their allergies worsen over time. That's especially true of allergies to foods, latex, or bee stings, which can result in more serious reactions with each exposure. Other things also make a big difference. All it takes is a heavy pollen season, or a new job in a moldy building, for allergies to flare up. If your allergy symptoms seem worse, there could be another reason. You might now have a second allergy -- or third or fourth. Having one allergy makes you more likely to get others. So if one year your ragweed symptoms seem more severe, it might be a reaction to another allergen that's also in the air. Allergies can interact in unexpected ways. For instance, up to a third of people who are allergic to pollens also have allergies to foods that have similar proteins in them, like certain vegetables and fruits. Doctors call this “oral allergy syndrome. You could have more severe allergic reactions if you're exposed to both at once -- for instance, if you eat a banana at the height of ragweed allergy season.
The key is to manage your symptoms and let your doctor know if you notice changes.
You might blame your triggers -- the pollen in the air, your best friend's cat -- for your symptoms.
But actually, most of those things are harmless. What really causes allergic reactions is your immune system. It mistakes innocent things in your surroundings for a serious threat and attacks them. The symptoms you get are the result.
Your odds of developing an allergy start in your genes. While specific allergies are not inherited, a tendency toward having allergies is. Children with one allergic parent have a 33% chance of developing allergies. With two allergic parents, it's a 70% chance. Even so, the circumstances have to be just right for something to trigger an allergic reaction. Other things may also be involved. For instance, if you come into contact with an allergen when you're weak, such as after a viral infection -- you might be more likely to develop an allergy to it. It begins with exposure. Even if you've been around a trigger (or “allergen,” as your doctor calls it) many times before with no trouble, your body may suddenly see it as an invader. If this happens, your immune system studies the allergen and makes antibodies against it, in case the same situation happens again. Then, the next time you come across that allergen, your immune system takes action. The antibodies recognize it and turn on special cells called mast cells. The mast cells burst open, releasing chemicals such as histamine that cause symptoms such as swelling. Swelling in your nasal passages might cause a runny nose. Swelling in the airways could cause asthma symptoms. Keep in mind that the amount of exposure can make a difference. If you're allergic to strawberries, you may have been able to eat one or two without symptoms. But once you eat three or four, you suddenly break out in hives. There's a tipping point -- or threshold -- for people with allergies. You can handle some exposure, but too much launches an immune system attack. The problem is that you can’t predict how you’ll recover. So if you have a food allergy, you should avoid your trigger foods completely.