Allergies are an overreaction of the body's natural defence system that helps fight infections (immune system). The immune system normally protects the body from viruses and bacteria by producing antibodies to fight them. In an allergic reaction, the immune system starts fighting substances that are usually harmless (such as dust mites, pollen, or a medicine) as though these substances 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 an allergy-producing substance (allergen). For example, the first time you are stung by a bee, you may have only pain and redness from the sting. If you are stung again, you may have hives or trouble breathing. This is caused by the response of the immune system.
Most people will have some problem with allergies or allergic reactions at some point in their lives. Allergic reactions can range from mild and annoying to sudden and life-threatening. Most allergic reactions are mild, and home treatment can relieve many of the symptoms. An allergic reaction is more serious when severe allergic reaction (anaphylaxis) occurs, when allergies cause other problems (such as nosebleeds, ear problems, wheezing, or coughing), or when home treatment doesn't help.
There are many types of allergies. Some of the more common ones include:
Seasonal allergies show up at the same time of the year every year and are caused by exposure to pollens from trees, grasses, or weeds. Hay fever is the most common seasonal allergy.
Allergies that occur for more than 9 months out of the year are called perennial allergies.
Use the Check Your Symptoms section to decide if and when you should see a doctor.
Health Tools help you make wise health decisions or take action to improve your health.
|Decision Points focus on key medical care decisions that are important to many health problems.|
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|Allergies: Should I take shots for insect sting allergies?|
|Actionsets are designed to help people take an active role in managing a health condition.|
|Allergies in Children: Giving an Epinephrine Shot to a Child|
|Allergies: Giving Yourself an Epinephrine Shot|
For tips to help relieve symptoms of an allergic reaction, see home treatment for:
For tips on how to treat dry and irritated skin, see the topic Dry Skin and Itching.
For information on how to treat an insect bite or sting, see the topic Insect Bites and Stings and Spider Bites.
Use the Check Your Symptoms section to evaluate your symptoms if any of the following occur during home treatment:
To prevent problems with severe allergic reactions:
To prevent seasonal or year-round allergy reactions:
Breast-feeding may prevent allergies. Breast-feed your baby for at least 6 months if possible to boost his or her immune system. Feeding only breast milk during the first 6 months of life may reduce the chances your child will develop food allergies or decrease the severity of your child's allergies. For more information, see the topic Breast-Feeding.
To prepare for your appointment, see the topic Making the Most of Your Appointment.
You can help your doctor diagnose and treat your condition by being prepared to answer the following questions:
|Primary Medical Reviewer||William H. Blahd, Jr., MD, FACEP - Emergency Medicine|
|Specialist Medical Reviewer||H. Michael O'Connor, MD - Emergency Medicine|
|Last Revised||July 19, 2011|
Last Revised: April 19, 2012
This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.