Anaphylaxis Symptoms and Diagnosis
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Anaphylaxis Symptoms and Diagnosis

Anaphylaxis Symptoms and Diagnosis
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Updated on August 14, 2025
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Anaphylaxis is a severe allergic reaction that usually affects multiple areas of the body at once.

Sam Torbati, MD, a cochair and the medical director of the emergency department at Cedars-Sinai in Los Angeles, explains that anaphylaxis may start with scratchiness in your throat, or a cough or wheeze, and in some cases can lead to constriction of the airway. It can also manifest as hives or rash, or even cause abdominal pain. A severe anaphylactic reaction can impact the cardiovascular system, causing low blood pressure, shock, or passing out, adds Dr. Torbati.

Anaphylaxis can be caused by a number of different allergens or triggers, including foods, medications, latex, and insect venom, among others. Here, we dive deeper into symptoms of anaphylaxis and the diagnostic process.

Illustrative graphic titled How Anaphylaxis Affects the Body shows Nasal Congestion, Face and Tongue Swelling, Throat Tightness, Trouble Breathing, Wheezing, Rash or Hives, Flushed or Pale Skin, Nausea or Vomiting, Weak or Rapid Pulse.Everyday Health logo
Anaphylaxis is a severe allergic reaction that can cause any of these symptoms shortly after you’re exposed to a trigger.

Signs of Anaphylaxis

Anaphylaxis symptoms typically begin within 5 to 30 minutes after you come into contact with an allergen.

 Less commonly, it can take an hour or longer for anaphylaxis to develop.
Symptoms of anaphylaxis typically affect more than one part of your body. They may include:

  • Red rash with hives or welts that are usually itchy
  • Flushed or pale skin
  • Swollen throat
  • Swelling of your face, eyes, tongue, or other areas of your body
  • Wheezing or coughing
  • Chest tightness or trouble breathing
  • Hoarse voice
  • Nasal congestion
  • Trouble swallowing
  • Nausea or vomiting
  • Diarrhea
  • Stomach cramps
  • Weak or rapid pulse
  • Dizziness or fainting
  • Heart palpitations
  • Anxiety or a sense of impending doom
  • Loss of consciousness

Anaphylaxis can progress quickly, with some people collapsing, no longer breathing, having seizures, or losing consciousness within one to two minutes. In these severe cases, the reaction can be fatal unless emergency care is immediately available.

If you suspect anaphylaxis, epinephrine (adrenaline) should be given as soon as possible, as it can reduce or reverse life-threatening symptoms, such as tongue or throat swelling, and help maintain heart function. Epinephrine is administered through an injection or nasal spray.

 The person experiencing anaphylaxis should still go to the nearest emergency room after receiving epinephrine.

Anaphylactic Shock

Anaphylaxis can lead to shock, a biological reaction involving dangerously low blood pressure and a rapid, weak pulse.

Shock can also cause confusion and cold, sweaty skin. “It can be life-threatening, involve severe respiratory symptoms or a sudden drop in blood pressure,” says Torbati. Not all cases of anaphylaxis lead to shock, but those that do are especially dangerous.

Regardless of whether you experience shock, an anaphylactic reaction requires immediate attention and emergency medical care.

How Anaphylaxis Is Diagnosed

In an emergency situation, your doctor will quickly diagnose anaphylaxis according to visible symptoms and immediately treat you.

This is because time is of the essence, and it would be a risk to your life to try to confirm an anaphylactic reaction with lab tests before administering treatment.

A rapid diagnosis of anaphylaxis is made on the basis of one of two scenarios.

If it is unknown whether you were exposed to an allergen and you have rapidly developing hives or other skin symptoms, a provider will look for at least one of the following:

  • Respiratory symptoms such as shortness of breath, wheezing, low blood oxygen levels, or persistent cough or throat-clearing
  • Hypotension, or low blood pressure
  • Symptoms that indicate your organ function is impaired, for example your muscles are soft and flabby, you’re fainting, or incontinent
If it is known or likely that you were exposed to an allergen, your provider will look for at least two of the following:

  • Symptoms affecting your skin such as rash, hives, itchiness, reddening of the skin, or swelling of the face, lips, tongue, or uvula
  • Respiratory symptoms such as shortness of breath, wheezing, low blood oxygen levels, or persistent cough or throat-clearing
  • Hypotension 
  • Gastrointestinal symptoms such as vomiting or painful cramps
If your symptoms are relatively mild and don’t clearly indicate anaphylaxis, your doctor may order one or more blood or urine tests. These tests measure levels of certain chemicals that your immune system produces during an allergic reaction. But these tests are usually unnecessary in an emergency situation — the priority is rapid treatment.

When possible, it’s important to make sure your symptoms aren’t caused by another condition if they don’t clearly indicate anaphylaxis. That’s because another condition may also require urgent treatment, and could be made worse by anaphylaxis treatment.

Conditions that could be mistaken for anaphylaxis include:

  • Generalized hives or swelling
  • Shock caused by cardiovascular issues (cardiogenic or hypovolemic shock)
  • Fainting (due to nonallergic factors)
  • Certain endocrine problems (carcinoid syndrome or pheochromocytoma)
  • Foreign object stuck in the airway
  • Pulmonary embolism (a blood clot in the lungs)
  • Autonomic epilepsy or seizure disorder
  • Stroke
  • Drug overdose
  • Monosodium glutamate or sulfite ingestion
  • Reaction to vancomycin infusion
  • Leukemia
  • Flushing syndromes
  • Vocal cord dysfunction
  • Panic attack

The list of possible conditions that share the symptoms of anaphylaxis would be in the hundreds, says Torbati. But, “most of the time it’s not a difficult diagnosis. If the history is there, like an insect bite or an exposure to a known allergen, diagnosis becomes simple.”

After emergency care for anaphylaxis, it’s a good idea to follow up with an allergist who can evaluate your risk of anaphylaxis generally and help figure out whether any previous symptoms were related to the condition. Your doctor will investigate all potential causes of your symptoms. This may involve allergy tests as well as tests for other health conditions.

To determine what to test for, your doctor will likely ask you about the symptoms and situations involved in past allergic reactions, even if your response didn’t involve anaphylaxis.

If you or your child has a severe allergy attack or has experienced signs of anaphylaxis in the past — even if the event seemed isolated — it’s a good idea to see an allergist to ensure you have a plan to avoid potential triggers and treat anaphylaxis if it occurs.

Additional reporting by Nina Wasserman.

The Takeaway

  • Anaphylaxis is a severe allergic reaction that usually affects multiple areas of the body at once.
  • It typically starts 5 to 30 minutes after exposure and can present as a rash, mild to severe respiratory distress, low blood pressure, or digestive symptoms such as abdominal pain. Some anaphylactic reactions can lead to shock, a reaction involving dangerously low blood pressure and a rapid, weak pulse.
  • The first-line treatment for anaphylaxis is epinephrine (adrenaline), followed by emergency medical care.
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Anaphylaxis. American Academy of Allergy, Asthma, and Immunology.
  2. Anaphylaxis. Mayo Clinic. April 16, 2025.
  3. Anaphylaxis. MedlinePlus. March 31, 2024.
  4. What Is Epinephrine? Allergy & Asthma Network.
  5. Low Blood Pressure. Mayo Clinic. June 13, 2024.
  6. McLendon K et al. Anaphylaxis. StatPearls. January 26, 2023.
  7. Carcinoid Syndrome. Mayo Clinic. April 30, 2025.
  8. Pheochromocytoma. Mayo Clinic. May 8, 2025.
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Jon E. Stahlman, MD

Medical Reviewer
Castle Connolly Top Doctor

Jon E. Stahlman, MD, has been a practicing allergist for more than 25 years. He is currently the section chief of allergy and immunology at Children’s Healthcare of Atlanta's Scottish Rite campus and the senior physician at The Allergy & Asthma Center in Atlanta. He served as the president of the Georgia Allergy Society, has been named a Castle Connolly Top Doctor, and was listed as a Top Doctor by Atlanta magazine. His research interests include new therapies for asthma and allergic rhinitis as well as the use of computerized monitoring of lung function.

He received his bachelor's and medical degrees from Emory University. He completed his pediatric residency at Boston Children’s Hospital and his fellowship in allergy and clinical immunology at Harvard University’s Boston Children’s Hospital and Brigham and Women’s Hospital. After his training, Dr. Stahlman conducted two years of clinical research at Boston Children’s Hospital and was part of the faculty at Harvard Medical School, where he taught medical students and allergy and immunology fellows.

Stahlman is board-certified and recertified in allergy and clinical immunology. He served as a principal investigator on phase 2 through 4 studies that are responsible for most of the U.S. Food and Drug Administration–approved therapies for allergies and asthma available today.

Outside of the office, he centers his interests around his wife and three daughters, coaching soccer for many years, and his hobbies include cycling and triathlons.

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Quinn Phillips

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A freelance health writer and editor based in Wisconsin, Quinn Phillips has a degree in government from Harvard University. He writes on a variety of topics, but is especially interested in the intersection of health and public policy. Phillips has written for various publications and websites, such as Diabetes Self-Management, Practical Diabetology, and Gluten-Free Living, among others.

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