Allergic Reaction - Topic Overview
Allergic Reaction Guide
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Allergies are an overreaction of the body'snatural defense system that helps fight infections (immune system).The immune system normally protects the body from viruses and bacteria byproducingantibodies to fight them. In anallergic reaction, the immune system starts fightingsubstances that are usually harmless (such asdust mites, pollen, or a medicine) as though thesesubstances were trying to attack the body. This overreaction can cause a rash,itchy eyes, a runny nose, trouble breathing, nausea, and diarrhea.
An allergic reaction may not occur the first time you are exposed to anallergy-producing substance (allergen). For example, the first timeyou are stung by a bee, you may have only pain and redness from the sting. Ifyou are stung again, you may havehives or trouble breathing. This is caused by theresponse of the immune system.
Many people will have some problemwith allergies or allergic reactions at some point in their lives. Allergicreactions can range from mild and annoying to sudden and life-threatening. Mostallergic reactions are mild, and home treatment can relieve many of thesymptoms. An allergic reaction is more serious when severe allergic reaction(anaphylaxis) occurs, whenallergies cause other problems (such as nosebleeds,ear problems, wheezing, or coughing), or when home treatment doesn'thelp.
Allergies often occur along with other diseases, such asasthma,ear infections,sinusitis, andsleep apnea. For more information, see the topicAllergic Rhinitis.
There are many types of allergies. Some of the more common ones include:
- Food allergies, which are more common in children than adults. Food allergies are most common in people who have an inherited tendency to develop allergic conditions. These people are more likely to have asthma and other allergies. For more information, see the topic Food Allergies.
- Medicine allergies. Many prescription and nonprescription medicines can cause an allergic reaction. Allergic reactions are common and unpredictable. The seriousness of the allergic reaction caused by a certain medicine will vary.
- Allergies to insect venom. When you are stung by an insect, poisons and other toxins in the insect's venom enter your skin. It is normal to have some swelling, redness, pain, and itching at the site of a sting. An allergic reaction to the sting occurs when your body's immune system overreacts to the venom of stinging insects. For more information, see the topic Allergies to Insect Stings.
- Allergies to animals, which are more likely to cause breathing problems than skin problems. You may be allergic to your pet's dead skin (dander), urine, dried saliva, or hair.
- Allergies to natural rubber (latex). Some people develop allergic reactions after repeated contact with latex, especially latex gloves.
- Allergies that develop from exposure to a particular inhaled substance in the workplace. These are called occupational asthma.
- Allergies to cosmetics, such as artificial nails, hair extensions, and henna tattoos.