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Allergic Reaction

Overview

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.

Types of allergies

There are many types of allergies. Some of the more common ones include:

  • Food allergies. They 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.
  • Medicine allergies. Many prescription and nonprescription medicines can cause an allergic reaction. These reactions are common and unpredictable. How serious the reaction is will depend on the type of medicine.
  • Allergies to insect venom. When you are stung by an insect, poisons and other toxins in the insect's venom enter your skin. It's 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.
  • Allergies to animals. These 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 allergies may be called occupational asthma.
  • Allergies to cosmetics, such as artificial nails, hair extensions, and henna tattoos.

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.

Health Tools

Health Tools help you make wise health decisions or take action to improve your health.

Actionsets are designed to help people take an active role in managing a health condition.

Check Your Symptoms

Are you concerned about an allergic reaction?
Yes
Allergic reaction concerns
No
Allergic reaction concerns
How old are you?
Less than 12 years
Less than 12 years
12 years or older
12 years or older
Are you male or female?
Male
Male
Female
Female

The medical assessment of symptoms is based on the body parts you have.

  • If you are transgender or nonbinary, choose the sex that matches the body parts (such as ovaries, testes, prostate, breasts, penis, or vagina) you now have in the area where you are having symptoms.
  • If your symptoms aren’t related to those organs, you can choose the gender you identify with.
  • If you have some organs of both sexes, you may need to go through this triage tool twice (once as "male" and once as "female"). This will make sure that the tool asks the right questions for you.
Could you be having a severe allergic reaction?
This is more likely if you have had a bad reaction to something in the past.
Yes
Possible severe allergic reaction (anaphylaxis)
No
Possible severe allergic reaction (anaphylaxis)
Do you have symptoms of shock?
Yes
Symptoms of shock
No
Symptoms of shock
Have you ever had a severe allergic reaction?
A severe allergic reaction affects the whole body. Your doctor may have called it anaphylaxis.
Yes
History of severe allergic reaction
No
History of severe allergic reaction
Have you been exposed to the same thing (called an allergen) or something similar to it that caused a severe reaction in the past?
For example, an allergen could be an insect, a certain food, or a type of medicine or drug.
Yes
Reexposed to substance that caused past severe reaction
No
No new exposure to substance that caused past severe reaction
Not sure
Possibly reexposed to substance that caused past severe reaction
In the past 2 days, were you exposed to that same allergen, and are you now having symptoms of an allergic reaction?
Even if the symptoms do not start right away or are mild at first, they may quickly become severe.
Yes
History of severe reaction with symptoms now
No
History of severe reaction with symptoms now
Are you having trouble breathing (more than a stuffy nose)?
Yes
Difficulty breathing more than a stuffy nose
No
Difficulty breathing more than a stuffy nose
Is there any new swelling?
Yes
New swelling
No
New swelling
Are the lips, tongue, mouth, or throat swollen?
Yes
Swelling of lips, tongue, mouth, or throat
No
Swelling of lips, tongue, mouth, or throat
Did the lips, tongue, mouth, or throat swell quickly?
Yes
Rapid swelling of lips, tongue, mouth, or throat
No
Rapid swelling of lips, tongue, mouth, or throat
Does swelling involve the palms of the hands, the soles of the feet, or the area from one large joint to another, such as from the ankle to the knee?
Yes
Swelling is across two joints, on soles of feet, or on palms of hands
No
Swelling is across two joints, on soles of feet, or on palms of hands
Is the swelling getting worse (over hours or days)?
Yes
Swelling is getting worse
No
Swelling is getting worse
Did you get an epinephrine shot to treat the reaction?
Yes
Has had epinephrine shot
No
Has had epinephrine shot
Is most of your body covered in hives?
Hives are raised, red, itchy patches of skin. They usually have red borders and pale centers. They may seem to move from place to place on the skin.
Yes
Hives covering most of body
No
Hives covering most of body
Did the hives appear within the past 3 hours?
Yes
Hives appeared within past 3 hours
No
Hives appeared within past 3 hours
Are there any symptoms of infection?
Yes
Symptoms of infection
No
Symptoms of infection
Do you think you may have a fever?
Yes
Possible fever
No
Possible fever
Are there red streaks leading away from the area or pus draining from it?
Yes
Red streaks or pus
No
Red streaks or pus
Do you have diabetes, a weakened immune system, peripheral arterial disease, or any surgical hardware in the area?
"Hardware" includes things like artificial joints, plates or screws, catheters, and medicine pumps.
Yes
Diabetes, immune problems, peripheral arterial disease, or surgical hardware in affected area
No
Diabetes, immune problems, peripheral arterial disease, or surgical hardware in affected area
Does your skin itch?
Yes
Itchy skin
No
Itchy skin
Is the itching severe?
Severe means that you are scratching so hard that your skin is cut or bleeding.
Yes
Severe itching
No
Severe itching
Has the itching interfered with sleeping or normal activities for more than 2 days?
Yes
Itching has disrupted sleep or normal activities for more than 2 days
No
Itching has disrupted sleep or normal activities for more than 2 days
Could you be having an allergic reaction to a medicine or a vaccine?
Almost any medicine or vaccine can cause an allergic reaction. Think about whether the problem started soon after you began using a new medicine or a higher dose of a medicine. Or did it start after you got a shot or vaccine?
Yes
Medicine or vaccine may be causing allergic reaction
No
Medicine or vaccine may be causing allergic reaction
Have your symptoms lasted longer than 2 weeks?
Yes
Symptoms for more than 2 weeks
No
Symptoms for more than 2 weeks

Many things can affect how your body responds to a symptom and what kind of care you may need. These include:

  • Your age. Babies and older adults tend to get sicker quicker.
  • Your overall health. If you have a condition such as diabetes, HIV, cancer, or heart disease, you may need to pay closer attention to certain symptoms and seek care sooner.
  • Medicines you take. Certain medicines, such as blood thinners (anticoagulants), medicines that suppress the immune system like steroids or chemotherapy, herbal remedies, or supplements can cause symptoms or make them worse.
  • Recent health events, such as surgery or injury. These kinds of events can cause symptoms afterwards or make them more serious.
  • Your health habits and lifestyle, such as eating and exercise habits, smoking, alcohol or drug use, sexual history, and travel.

Try Home Treatment

You have answered all the questions. Based on your answers, you may be able to take care of this problem at home.

  • Try home treatment to relieve the symptoms.
  • Call your doctor if symptoms get worse or you have any concerns (for example, if symptoms are not getting better as you would expect). You may need care sooner.

Symptoms of infection may include:

  • Increased pain, swelling, warmth, or redness in or around the area.
  • Red streaks leading from the area.
  • Pus draining from the area.
  • A fever.

Symptoms of a severe allergic reaction (anaphylaxis) may include:

  • The sudden appearance of raised, red areas (hives) all over the body.
  • Rapid swelling of the throat, mouth, or tongue.
  • Trouble breathing.
  • Passing out (losing consciousness). Or you may feel very lightheaded or suddenly feel weak, confused, or restless.

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:

  • You may feel a little out of breath but still be able to talk (mild difficulty breathing), or you may be so out of breath that you cannot talk at all (severe difficulty breathing).
  • It may be getting hard to breathe with activity (mild difficulty breathing), or you may have to work very hard to breathe even when you’re at rest (severe difficulty breathing).

Certain health conditions and medicines weaken the immune system's ability to fight off infection and illness. Some examples in adults are:

  • Diseases such as diabetes, cancer, heart disease, and HIV/AIDS.
  • Long-term alcohol and drug problems.
  • Steroid medicines, which may be used to treat a variety of conditions.
  • Chemotherapy and radiation therapy for cancer.
  • Other medicines used to treat autoimmune disease.
  • Medicines taken after organ transplant.
  • Not having a spleen.

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:

  • Passing out (losing consciousness).
  • Feeling very dizzy or lightheaded, like you may pass out.
  • Feeling very weak or having trouble standing.
  • Not feeling alert or able to think clearly. You may be confused, restless, fearful, or unable to respond to questions.

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:

  • Passing out (losing consciousness).
  • Being very sleepy or hard to wake up.
  • Not responding when being touched or talked to.
  • Breathing much faster than usual.
  • Acting confused. The child may not know where he or she is.

Make an Appointment

Based on your answers, the problem may not improve without medical care.

  • Make an appointment to see your doctor in the next 1 to 2 weeks.
  • If appropriate, try home treatment while you are waiting for the appointment.
  • If symptoms get worse or you have any concerns, call your doctor. You may need care sooner.

Seek Care Today

Based on your answers, you may need care soon. The problem probably will not get better without medical care.

  • Call your doctor today to discuss the symptoms and arrange for care.
  • If you cannot reach your doctor or you don't have one, seek care today.
  • If it is evening, watch the symptoms and seek care in the morning.
  • If the symptoms get worse, seek care sooner.

Seek Care Now

Based on your answers, you may need care right away. The problem is likely to get worse without medical care.

  • Call your doctor now to discuss the symptoms and arrange for care.
  • If you cannot reach your doctor or you don't have one, seek care in the next hour.
  • You do not need to call an ambulance unless:
    • You cannot travel safely either by driving yourself or by having someone else drive you.
    • You are in an area where heavy traffic or other problems may slow you down.

Call 911 Now

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.

Seek Care Now

Based on your answers, you may need care right away. The problem is likely to get worse without medical care.

  • Call your doctor now to discuss the symptoms and arrange for care.
  • If you cannot reach your doctor or you don't have one, go to the emergency room now. You may have a reaction after the epinephrine wears off.
  • You do not need to call an ambulance unless:
    • You cannot travel safely either by driving yourself or by having someone else drive you.
    • You are in an area where heavy traffic or other problems may slow you down.

Self-Care

Here are some things you can do at home to help your allergies.

  • Avoid contact with whatever is causing the itching.

    If you know what's causing the itching or hives, then you can try to stay away from the irritant.

  • Treat a sore throat.

    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.

  • Treat hay fever or seasonal allergies.

    Use saline drops or a humidifier to help clear a stuffy nose. Or take an allergy medicine that's specific to your symptoms.

  • Look out for mold.

    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.

  • Be aware of indoor allergies.

    Newer, energy-saving homes that are built with double- or triple-paned windows and more insulation keep heat and allergens indoors.

  • Don't forget about animal allergies.

    When allergies are worse around pets or animals, symptoms may be caused by your pet's dead skin (dander), urine, dried saliva, or hair.

  • Try antihistamines.

    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.

  • Try lotions or creams.

    Calamine lotion or hydrocortisone cream applied to the skin may help relieve itching.

When to call for help during self-care

Call a doctor if any of the following occur during self-care at home:

  • New or worse trouble breathing, wheezing, or tightness in the chest.
  • New or worse swelling of the throat, tongue, lips, or mouth.
  • New or worse hives.
  • New or worse skin swelling.
  • New or worse signs of infection, such as redness, warmth, pus, or a fever.
  • Symptoms occur more often or are more severe.

Learn more

Preparing For Your Appointment

Credits

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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