by Tayla Hollman

Allergies are extremely common in the United States, with more than 50 million Americans experiencing different types of allergies throughout the year, according to the American College of Allergy, Asthma & Immunology (ACAAI). Allergies can range from mild to severe, and if they aren't treated quickly, some allergic reactions can be life-threatening. That's why it is of the utmost importance to know when to visit the emergency room for an allergic reaction.

What are the different types of allergic reactions?

"An allergic reaction is a hypersensitive reaction that your immune system has to a certain substance," says Dr. Josephin Mathai, medical director of the emergency department at HCA Florida St. Lucie Hospital. "Every person can have a different trigger, and the level of reaction you have is different for everybody."

Shellfish is the most common allergen for adults, followed by peanuts and tree nuts, according to the Asthma and Allergy Foundation of America (AAFA). For children, the most common allergens are milk, eggs and peanuts. Some people may have only a mild reaction if they are exposed to an allergen, while others may have a more severe reaction.

There are four main types of allergic reactions:

  1. Anaphylactic: Symptoms appear within a few seconds to minutes.
  2. Cytotoxic: Symptoms appear within a few minutes to hours.
  3. Immune complex: Symptoms set in after several hours.
  4. Cell mediated (delayed): Symptoms set in after several hours or days.

What are the symptoms of an allergic reaction?

The symptoms of an allergic reaction vary and typically develop within a few minutes of exposure to an allergen. Potential symptoms include:

  • Sneezing and a blocked, itchy or runny nose
  • Itchy, red and watering eyes
  • Rash (hives)
  • Wheezing, shortness of breath or cough
  • Nausea or vomiting
  • Diarrhea
  • Abdominal pain or cramping

For many people, the symptoms of an allergic reaction will go away within a few hours or days with either Benadryl or a combination of Benadryl and steroids. But having more than one of these symptoms at a time can be cause for concern. "Whenever there is multi-symptom involvement, like you have a rash and you're vomiting, or you have a rash and you start to have chest pain or dizziness, that always points toward a much more significant reaction," Dr. Mathai says.

When to go to the ER for an allergic reaction

Many allergic reactions are mild and won't require a trip to the emergency room. "Allergic reactions are kind of like a spectrum," Dr. Mathai says. "If you have a simple rash, and you're itching, you can probably go to urgent care. But if you have a rash and vomiting, you should go to the ER."

An anaphylactic allergic reaction can be life-threatening and requires immediate medical treatment. If you or someone else is experiencing an anaphylactic allergic reaction, the first course of action should be to administer epinephrine (via an EpiPen) if it is available. Epinephrine helps bring blood to your vessels and opens up your airways if you are having trouble breathing. If an EpiPen is not available, go to an ER right away. You will still need to call 911 or go to the ER after administering epinephrine because one injection may not be enough, and you may have a delayed reaction, according to Dr. Mathai.

"Anytime your breathing is compromised, or you feel like your face or tongue are starting to swell up, or you start to have stridor — that squeaky kind of breathing — you need to make sure you're calling 911 and getting to the nearest emergency room," she adds. If you're having trouble breathing, an ER is your best bet because urgent care doesn't have the capacity to intubate, which is when a tube is inserted through the mouth or nose and then down into the windpipe.

Another sign that you should go to the ER for an allergic reaction is when it comes with gastrointestinal issues. "GI symptoms, which are vomiting or diarrhea, can be part of anaphylaxis and part of the anaphylactic shock reaction," Dr. Mathai says. "If you're experiencing that along with a rash, you need to go to the emergency room. That's more than one system involvement."

How to avoid an allergic reaction

If you know what your allergy triggers are, it is important to avoid them as much as possible to prevent an allergic reaction. You should also be sure to carry an EpiPen just in case you are exposed to an allergen and have a severe reaction. However, many patients who go to an ER don't know what their triggers are, so it can be difficult for doctors to pinpoint the cause of the reaction. "It could be anything from detergents to soap to something you ate or something environmental," Dr. Mathai says. "But if you had an allergic reaction that was significant enough for you to come to the emergency room, then you need to make sure you see an allergist and get a full panel of tests, and then you can know what your triggers are."

Knowing when to go to the ER for an allergic reaction can save your life, or the life of a loved one. If you do visit the ER for an allergic reaction, expect to stay there for at least four hours to make sure your symptoms are under control.