How Long Is an Allergic Reaction?

Reviewed on 6/4/2022
An elder woman with red, swollen lips caused by allergic reaction
Many substances can cause allergic reactions and the length of time a reaction lasts may depend on the substance. Allergic reactions can be caused by drugs, certain foods, insect stings/bites, latex, mold, pet dander, and pollen.

Allergic reactions happen when the body’s immune system has a reaction to a substance it sees as harmful, called an allergen

Many substances can cause allergic reactions and the length of time a reaction lasts may depend on the substance. 

  • Drugs
    • Drug reactions such as hives may be acute and last fewer than six weeks, or it they can become chronic and last six weeks or more
    • Hives may come and go but individual welts rarely remain on the skin for more than 24 hours
    • A morbilliform drug eruption may not appear for one or two weeks after starting a new medication and can last for several days to weeks after discontinuing the medication, then it fades
  • Certain foods
    • Symptoms of food allergies usually start as soon as a few minutes after consuming a food, up to about two hours after eating 
    • Sometimes after the first symptoms go away a second wave of symptoms returns one to four hours later (biphasic reaction) 
  • Insect stings/bites
    • Most of the time these reactions persist for two to three days
  • Latex
    • The allergic reaction usually begins within five to 15 minutes after coming into contact with latex but it can be delayed for several hours
    • Symptoms may persist for several hours to days after latex contact has ceased
  • Mold
    • Symptoms usually appear within two to nine hours after exposure and last for one to three days
  • Pet dander
    • Pet allergens can collect on furniture and other surfaces and do not lose their strength for a long time
    • If allergen levels are low or a person is only minimally sensitive, symptoms may not appear until after several days of contact with the pet
    • Highly sensitive people who inhale airborne particles may cough, wheeze, and have shortness of breath within 15 to 30 minutes of inhaling the allergens
  • Pollen
    • Allergies occur at the same time every year and last as long as the allergen is in the air (usually two to three weeks per allergen)

What Are Symptoms of an Allergic Reaction?

Symptoms of an allergic reaction include:

  • Itchy, watery eyes
  • Itchy nose
  • Runny nose
  • Sneezing
  • Swelling
  • Skin redness
  • Skin itching 
  • Hives 
  • Rashes
  • Bloating
  • Stomach cramping
  • Vomiting
  • Diarrhea
  • Cough
  • Pain

Call 911 and get to a hospital’s emergency department if you experience any symptoms of anaphylaxis, a severe and potentially life-threatening allergic reaction: 

  • Swelling of the lips, tongue, or throat (throat closing)
  • Shortness of breath
  • Wheezing 
  • Chest tightness
  • Dizziness, lightheadedness, and/or fainting
  • Severe skin rashes, itching, or hives
  • Stomach pain, bloating, vomiting or diarrhea
  • Uterine cramps
  • Sense that something awful is about to happen

How Are Allergic Reactions Diagnosed?

Allergies are diagnosed with a physical examination and medical history. Tests to determine allergens include: 

  • Skin prick test (SPT)
  • Intradermal skin test 
  • Blood tests (specific IgE)
  • Physician-supervised challenge tests 
  • Patch test

What Is the Treatment for Allergic Reactions?

The main treatment for allergic reactions is to prevent them by avoiding known allergens when possible. 

To reduce symptoms of airborne allergens, wash out your nose daily with a squeeze bottle filled with nasal saline rinse or by using a Neti pot.

Medicines to treat symptoms of an allergic reaction include:  

  • Nasal corticosteroids for nasal allergies
  • Antihistamines for seasonal and indoor allergies
  • Mast cell stabilizers to help with itchy, watery eyes or an itchy, runny nose
  • Decongestants to reduce stuffiness
    • Do not use nasal decongestant sprays more than three days in a row or you may experience a rebound reaction, where symptoms get worse
  • Corticosteroid creams or ointments to relieve skin itching and rash
  • Oral corticosteroids to reduce swelling and stop severe allergic reactions 
  • Epinephrine
    • May be prescribed for life-threatening anaphylaxis (severe allergic reaction)
    • Usually in the form of an epinephrine auto-injector “pen” device
    • Must be used within minutes of the first sign of serious allergic reaction
    • For life-threatening allergic reactions to food, insect stings, latex, and medications 
Reviewed on 6/4/2022
Image Source: iStock Images