Anaphylactic shock is a rare but severe allergic reaction that can be deadly if you don’t treat it right away. It’s most often caused by an allergy to food, insect bites, or certain medications.

A shot of a drug called epinephrine is needed immediately, and you should call 911 for emergency medical help.

The terms “anaphylaxis” and “anaphylactic shock” are often used to mean the same thing. They both refer to a severe allergic reaction. Shock is when your blood pressure drops so low that your cells (and organs) don’t get enough oxygen. Anaphylactic shock is shock that’s caused by anaphylaxis.

You typically notice the first symptoms within 15 minutes of coming into contact with the thing you’re allergic to. They may start out mild, like a runny nose or an uneasy feeling. But they can get much worse very fast. Some typical symptoms include:

• Swelling of your mouth
• Tight feeling in your throat and difficulty breathing
• Hives
• Vomiting
• Dizziness
• Fainting
• Rapid heartbeat

In severe cases, people collapse, stop breathing, and lose consciousness in just a couple of minutes.

A shot of epinephrine in your thigh is needed right away, and you should call 911 because you’re at risk for a second reaction (called a biphasic reaction) within 12 hours. At the emergency room, doctors can keep an eye on your symptoms and treat you in case of a second reaction.

If you don’t have epinephrine, emergency room doctors can save your life. They’ll put a shot of epinephrine under your skin or in a muscle or vein. Usually this gets your blood pressure, which drops during anaphylactic shock, back to normal. You’ll also get fluids, steroids, and antihistamines (drugs used to treat allergic reactions) through a tube connected to one of your veins until your symptoms are gone.