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Home > Health Library > Allergic Reaction
Allergies are an overreaction of the body's natural defense 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 to fight substances that are usually harmless, such as dust mites, pollen, or a medicine. It fights them 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're 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're stung again, you may have hives or trouble breathing. This is caused by the response of the immune system.
Many people will have some problem with allergies or allergic reactions at some point in their lives. Reactions can range from mild and annoying to sudden and life-threatening. Most allergic reactions are mild. Home treatment can relieve many of the symptoms. A reaction is more serious when a 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.
Allergies often occur along with other diseases, such as asthma, ear infections, sinusitis, and sleep apnea.
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. They 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.
Year-round symptoms (chronic allergies) are most likely to occur from exposure to animal dander, house dust, or mold.
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Many things can affect how your body responds to a symptom and what kind of care you may need. These include:
You have answered all the questions. Based on your answers, you may be able to take care of this problem at home.
Symptoms of infection may include:
Symptoms of a severe allergic reaction (anaphylaxis) may include:
A severe reaction can be life-threatening. If you have had a bad allergic reaction to a substance before and are exposed to it again, treat any symptoms as an emergency. Even if the symptoms are mild at first, they may quickly become very severe.
Symptoms of difficulty breathing can range from mild to severe. For example:
Certain health conditions and medicines weaken the immune system's ability to fight off infection and illness. Some examples in adults are:
Shock is a life-threatening condition that may quickly occur after a sudden illness or injury.
Adults and older children often have several symptoms of shock. These include:
Shock is a life-threatening condition that may occur quickly after a sudden illness or injury.
Babies and young children often have several symptoms of shock. These include:
Based on your answers, the problem may not improve without medical care.
Based on your answers, you may need care soon. The problem probably will not get better without medical care.
Based on your answers, you may need care right away. The problem is likely to get worse without medical care.
Based on your answers, you need emergency care.
Call 911 or other emergency services now.
If you have an epinephrine shot, use it while you wait for help to arrive. Follow the directions on the label about how to give the shot.
Sometimes people don't want to call 911. They may think that their symptoms aren't serious or that they can just get someone else to drive them. Or they might be concerned about the cost. But based on your answers, the safest and quickest way for you to get the care you need is to call 911 for medical transport to the hospital.
Here are some things you can do at home to help your allergies.
If you know what's causing the itching or hives, then you can try to stay away from the irritant.
A sore throat may be caused by postnasal drip. Adults and children who can gargle can try gargling with warm salt water at least once each hour to help ease throat soreness.
Use saline drops or a humidifier to help clear a stuffy nose. Or take an allergy medicine that's specific to your symptoms.
Allergies that are worse in damp weather may be caused by mold. Mold produces spores that move, like pollen, in outdoor air during warmer months. During winter months, indoor molds can also be a problem.
Newer, energy-saving homes that are built with double- or triple-paned windows and more insulation keep heat and allergens indoors.
When allergies are worse around pets or animals, symptoms may be caused by your pet's dead skin (dander), urine, dried saliva, or hair.
An antihistamine medicine, such as loratadine (Claritin), may help relieve itching, redness, and swelling. Don't give antihistamines to your child unless you've checked with the doctor first. Be safe with medicines. Read and follow all instructions on the label.
Calamine lotion or hydrocortisone cream applied to the skin may help relieve itching.
Call a doctor if any of the following occur during self-care at home:
You can help your doctor diagnose and treat your condition by being prepared for your appointment.
Current as of:
April 20, 2022
Author: Healthwise StaffMedical Review: William H. Blahd Jr. MD, FACEP - Emergency MedicineKathleen Romito MD - Family MedicineAdam Husney MD - Family MedicineE. Gregory Thompson MD - Internal Medicine
Current as of: April 20, 2022
Author: Healthwise Staff
Medical Review:William H. Blahd Jr. MD, FACEP - Emergency Medicine & Kathleen Romito MD - Family Medicine & Adam Husney MD - Family Medicine & E. Gregory Thompson MD - Internal Medicine
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