If you're with someone having an allergic reaction with signs of anaphylaxis:

• Immediately call 911 or your local medical emergency number.
• Ask the person if he or she is carrying an epinephrine autoinjector (EpiPen, Auvi-Q, others) to treat an allergic attack.
• If the person says he or she needs to use an autoinjector, ask whether you should help inject the medication. This is usually done by pressing the autoinjector against the person's thigh.
• Have the person lie still on his or her back.
• Loosen tight clothing and cover the person with a blanket. Don't give the person anything to drink.
• If there's vomiting or bleeding from the mouth, turn the person on his or her side to prevent choking.
• If there are no signs of breathing, coughing or movement, begin CPR. Do uninterrupted chest presses — about 100 every minute — until paramedics arrive.
• Get emergency treatment even if symptoms start to improve. After anaphylaxis, it's possible for symptoms to recur. Monitoring in a hospital for several hours is usually necessary.

If you're with someone having signs and symptoms of anaphylaxis, don't wait to see whether symptoms get better. Seek emergency treatment right away. In severe cases, untreated anaphylaxis can lead to death within half an hour.

An antihistamine pill, such as diphenhydramine (Benadryl), isn't sufficient to treat anaphylaxis. These medications can help relieve allergy symptoms, but work too slowly in a severe reaction.