What Are Allergies?
Allergies are abnormal immune system reactions to things that are typically harmless to most people. When you're allergic to something, your immune system mistakenly believes that this substance is harmful to your body. (Substances that cause allergic reactions — such as certain foods, dust, plant pollen, or medicines — are known as allergens.)
What Happens in Allergies?
In an attempt to protect the body, the immune system produces IgE antibodies to that allergen. Those antibodies then cause certain cells in the body to release chemicals into the bloodstream, one of which is histamine (pronounced: HIS-tuh-meen).
The histamine then acts on the eyes, nose, throat, lungs, skin, or gastrointestinal tract and causes the symptoms of the allergic reaction. Future exposure to that same allergen will trigger this antibody response again. This means that every time you come into contact with that allergen, you'll have some form of allergy symptoms.
What Are the Signs and Symptoms of Allergies?
Allergic reactions can be mild, like a runny nose, or they can be serious, like difficulty breathing (especially if you have a history of asthma).
Some types of allergies cause multiple symptoms. And in rare cases, an allergic reaction can become very severe — this is called anaphylaxis (pronounced: an-uh-fuh-LAK-sis). Signs of anaphylaxis include trouble breathing or swallowing; swelling of the lips, tongue, and throat or other parts of the body; and dizziness or loss of consciousness.
Anaphylaxis usually happens minutes after exposure to a trigger, such as a peanut, but some reactions can be delayed by as long as 4 hours. Luckily, anaphylactic reactions don't happen often and can be treated successfully.
What Causes Allergies?
The tendency to develop allergies is often hereditary, which means it can be passed down through your genes. However, just because a parent or sibling has allergies doesn't mean you will definitely get them, too. A person usually doesn't inherit a particular allergy, just the likelihood of having allergies.
What Things Are People Allergic to?
Some of the most common allergens are:
Airborne particles. Often called environmental allergens, these are the most common allergens. Airborne particles that can cause allergies include dust mites (tiny bugs that live in house dust); mold spores; animal dander (flakes of scaly, dried skin) and dried saliva from your pets; and pollen from grass, ragweed, and trees.
Foods. Food allergies are most common in babies and may go away as people get older. Although some food allergies can be serious, many just cause annoying symptoms like an itchy rash, a tingly tongue, and diarrhea. The most common food allergies are: milk and other dairy products, eggs, wheat, soy, peanuts and tree nuts, and seafood.
Insect stings. The venom (poison) in& insect stings can cause allergic reactions, and can be severe and even cause an anaphylactic reaction in some people.
Medicines. Antibiotics — medicines used to treat infections — are the most common type of medicines that cause allergic reactions. Many other medicines, including over-the-counter medications (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.