An allergy attack is your immune system overreacting to a substance that’s normally harmless, like pollen, pet dander, or a food protein. Instead of ignoring the substance, your body treats it as a threat and launches a defensive response that causes symptoms ranging from a runny nose and itchy eyes to, in severe cases, life-threatening swelling and breathing problems. The reaction can start within seconds of exposure or build over minutes to hours, depending on the trigger and your sensitivity.
What Happens Inside Your Body
An allergy attack is a case of mistaken identity. Your immune system flags a harmless substance (the allergen) as dangerous and produces a specific type of antibody called IgE to target it. These IgE antibodies latch onto mast cells, which are immune cells packed with chemical granules and stationed throughout your skin, airways, and gut. The first time you’re exposed, you may not notice anything. Your body is quietly arming itself.
The next time that same allergen enters your body, the IgE antibodies on your mast cells catch it like a hook. This switches the mast cells on, and they release their stored chemicals, primarily histamine, in a rapid burst called degranulation. Histamine is the main driver of allergy symptoms. It forces blood vessels open, floods tissues with fluid (causing swelling), ramps up mucus production, and triggers itching and irritation. All of this is your immune system trying to flush out a threat that was never actually dangerous.
Common Triggers
Allergy attacks fall into a few broad categories based on what sets them off:
- Airborne allergens: pollen, animal dander, dust mites, and mold. These are the most common triggers for seasonal and indoor allergies.
- Foods: peanuts, tree nuts, wheat, soy, fish, shellfish, eggs, and milk account for the majority of food allergy reactions.
- Insect stings: bee and wasp venom can trigger reactions ranging from localized swelling to full-body anaphylaxis.
- Medications: penicillin and related antibiotics are among the most frequent drug allergens.
- Contact allergens: latex and certain chemicals can cause skin reactions when touched.
The type of trigger often shapes the type of reaction. Airborne allergens typically cause respiratory and eye symptoms, while food allergens are more likely to involve the skin, gut, or multiple body systems at once.
Mild to Moderate Symptoms
Most allergy attacks stay localized, meaning the symptoms show up in one area of your body, usually wherever the allergen made contact. Breathing in pollen produces the classic hay fever pattern: runny nose, sneezing, and itchy, watery eyes. Skin contact with an allergen can cause hives (raised, itchy bumps) or eczema flare-ups with dry, red, irritated patches. Airborne triggers can also affect the lungs, leading to wheezing, coughing, and tightness in the chest, especially in people with allergic asthma.
These reactions are uncomfortable but not dangerous for most people. They tend to peak within 15 to 30 minutes of exposure and can last hours or even days if you’re still in contact with the trigger. Over-the-counter antihistamines work by blocking histamine from binding to your tissues, which is why they’re effective for these milder symptoms.
When a Reaction Becomes Severe
Anaphylaxis is the most dangerous form of an allergy attack. It involves multiple body systems at the same time and can escalate within minutes. Signs include swelling of the tongue, lips, or throat, difficulty breathing or talking, a hoarse voice, abdominal pain, vomiting, dizziness, and a drop in blood pressure that can lead to collapse. Unlike a mild reaction that stays in one area, anaphylaxis is systemic, meaning the flood of histamine affects your whole body at once.
Antihistamine pills are not fast enough to treat anaphylaxis. They can take 30 minutes or more to start working, which is too slow when airways are closing. Epinephrine (delivered through an auto-injector like an EpiPen) is the only first-line treatment. It works in the opposite direction of histamine: tightening blood vessels to restore blood pressure, relaxing airway muscles to open breathing passages, and reducing swelling in the throat and face. It acts within minutes.
How Fast Symptoms Develop
Allergy attacks typically begin within seconds to minutes of exposure, though food allergies can sometimes take up to two hours as the allergen is digested and absorbed. Insect sting and medication reactions tend to be the fastest, often hitting within five to ten minutes.
One pattern that catches people off guard is the biphasic reaction. This is a second wave of symptoms that returns after the initial reaction has resolved, even without any new exposure to the trigger. A systematic review of over 4,000 anaphylaxis cases found that when biphasic reactions occurred, symptoms came back at a median of 11 hours later, though the window ranged from as little as 12 minutes to as long as 72 hours. People who had low blood pressure during their initial reaction or whose trigger was unknown faced a higher risk of this rebound. This is one reason emergency departments often keep patients for observation after treating anaphylaxis.
What to Do During a Severe Reaction
If someone near you is showing signs of anaphylaxis, call emergency services immediately. Then check whether they carry an epinephrine auto-injector. If they do and need help, the device is pressed firmly against the outer thigh and held in place for several seconds. It works through clothing.
While waiting for paramedics, have the person lie flat on their back and stay still. Loosen any tight clothing and cover them with a blanket. If they’re vomiting or bleeding from the mouth, turn them onto their side to keep the airway clear. Don’t give them anything to drink. If they stop breathing or become unresponsive, start CPR with chest compressions at a rate of about 100 per minute until help arrives.
After the Attack: What Comes Next
A severe allergy attack shouldn’t end at the emergency room door. The recommended next step is developing a written emergency action plan that spells out your triggers, your medications, and exactly what to do if a reaction starts. Anyone at risk for anaphylaxis should carry an epinephrine auto-injector at all times and know how to use it. The standard adult dose is 0.3 mg for people weighing 66 pounds (30 kg) or more, with a lower 0.15 mg dose for children between 33 and 66 pounds.
A referral to an allergist is the logical follow-up, especially if the trigger isn’t clear. Allergists use detailed history-taking and skin or blood testing to confirm exactly which substances you react to. This matters because avoidance is still the most effective prevention strategy, and you can’t avoid something you haven’t identified. Many allergists also recommend medical alert jewelry so that bystanders and first responders know about your allergy in an emergency.
For people with milder, recurring allergy attacks from airborne triggers, long-term management often involves daily antihistamines, nasal corticosteroid sprays, or immunotherapy (allergy shots or sublingual tablets). Immunotherapy gradually retrains your immune system to tolerate the allergen, reducing the severity of reactions over months to years. It’s the closest thing to addressing the root cause rather than just managing symptoms.