Anaphylaxis is a potentially life-threatening allergic reaction. Anaphylaxis is known to have a rapid and unpredictable onset. Symptoms can start within minutes after exposure to an allergen, which is any substance that causes you to have an allergic response.

Biphasic anaphylaxis is a recurrence of anaphylaxis after appropriate treatment. It happens with no additional exposure to the allergen. Think of it as anaphylaxis, part two.

Anaphylaxis affects up to 2 percent of the population. The true incidence of biphasic anaphylaxis is unknown, but some studies report that it occurs in up to 20 percent of these cases.

Biphasic anaphylaxis strikes after you’ve survived the crisis of the initial attack and all seems well. The second attack can occur anywhere from 1 hour to 72 hours after the initial attack. It commonly happens within 8 to 10 hours. Due to the risk of biphasic anaphylaxis, your doctor may want you to stay in the hospital after the initial attack to monitor your condition.

The symptoms of biphasic anaphylaxis are the same as anaphylaxis. They may differ in severity, though. Symptoms of the second phase of anaphylaxis are typically mild or moderate. There’s no guarantee, however, that the second event won’t become a life-threatening one. Every episode requires immediate medical attention.

Both forms of anaphylaxis are frightening to experience. After exposure to an allergen, a series of events take place throughout your body:

  • Your skin becomes red, itchy, and may swell or produce hives.
  • Your airways begin to close, and breathing becomes increasingly difficult.
  • Your tongue and mouth swell.
  • Your blood pressure drops.
  • You may feel pain in your abdomen.
  • You may have diarrhea.
  • You may experience vomiting.
  • You may lose consciousness.
  • You may experience shock.

Both forms of anaphylaxis are medical emergencies and require immediate treatment, preferably in a hospital emergency room. If you don’t get treatment for anaphylaxis, it can be fatal.

The cause of biphasic anaphylaxis isn’t fully understood. There’s no accurate way to identify all people who are more likely to experience biphasic anaphylaxis, but risk factors include having:

  • a history of anaphylaxis
  • an allergy without a known cause
  • symptoms that include diarrhea or wheezing

Any allergen can cause anaphylaxis. Some allergens are more likely to trigger anaphylaxis, including:

  • antibiotics and nonsteroidal anti-inflammatory drugs (NSAIDS) such as aspirin, ibuprofen, and naproxen
  • foods, including peanuts, tree nuts, seafood, and eggs

Epinephrine, or adrenaline, is the main drug used to treat anaphylaxis. It’s fast and effective in opening your airways and reducing other symptoms. Epinephrine is available as an auto-injector. The person experiencing the attack or someone with them can administer the medication if medical help is not nearby. The brand most people are familiar with is EpiPen.

If it’s decided that you should carry an auto-injector, your doctor will give you a prescription for one and show you how it works. The device is easy to use:

  • Pull off the safety cap.
  • Firmly push the injector against the muscle or fleshy part of your outer thigh. This pressure will release the spring-loaded needle. You can administer the injection through clothing.
  • Keep the injector in place for several seconds before removing it.

Even if you feel better after the injection, it’s still important to seek medical help. If you have a history of severe allergic reactions, you should always carry an epinephrine auto-injector and know how to use it.

It’s critical to identify what caused the anaphylaxis so you can avoid it in the future. In some instances, your doctor may recommend immunotherapy, or allergy shots, which can reduce your body’s response to the allergen. If your doctor prescribes an epinephrine auto-injector, carry it with you. Show family members and other people how to use it, too.

Call 911 immediately if you or someone you are with is having an attack. Your goal is to get professional medical care as quickly as possible.

If you are with someone who is having an attack:

  • Ask if they have an EpiPen or other auto-injector.
  • If they have an auto-injector, inject them with the medication yourself if they cannot do it.
  • Help them get comfortable and elevate their legs, if possible.
  • If needed, perform CPR.