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How Fast Can Allergic Reactions Happen?

author image Genevieve Van Wyden
Genevieve Van Wyden began writing in 2007. She has written for “Tu Revista Latina” and owns three blogs. She has worked as a CPS social worker, gaining experience in the mental-health system. Van Wyden earned her Bachelor of Arts in journalism from New Mexico State University in 2006.
How Fast Can Allergic Reactions Happen?
With some allergies, you do not have much time to act. Photo Credit Jupiterimages/Comstock/Getty Images

With some allergic reactions, you don't have very much time between contact with the allergen and the reaction itself. Some reactions are severe and life-threatening, requiring that you get immediate medical help. If you or someone close to you has a severe allergy, it is important to know how these reactions develop and what to do.

Severe Reactions

An allergic reaction develops when your body is sensitive to a food such as peanuts, dairy or shellfish, or a medication such as penicillin. Allergic reactions involve your skin, eyes, airways, nose and digestive system.

Your allergic reaction to a substance can develop within minutes of coming into contact with the item. If your reaction is severe, it begins to develop within seconds, but some reactions take several hours to present themselves.

Reactions to Drugs

If you have an allergy to a drug such as penicillin, you must have been exposed to it in the past for your reaction to be a true allergic reaction. If you come into accidental contact with penicillin, you may develop a severe allergic reaction within minutes involving most areas of your body from your skin to your cardiovascular system. Different areas of your body begin to swell -- you may develop hives. Your blood pressure drops suddenly, leading to dizziness; you may pass out. If your reaction is severe enough, several internal organs may suffer damage, writes the Allergist website. Once anaphylaxis begins, you and others around you must act quickly to get the emergency medical help you need. While an antihistamine may help lessen the severity of your allergic reaction, you still need skilled medical care.

Your allergic reaction needs immediate medical treatment, including oxygen, adrenaline and an antihistamine. You may also be given fluids intravenously. While you are under medical care, your doctor may give you prescription steroids; if you stop breathing, you may be placed onto a ventilator.

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Allergens and Symptoms

Some substances to which you may be allergic include plants, medications, pet dander, nuts, shellfish, fish, insect stings and bites and plant pollens. Your reactions to some of these allergens may be mild while others are more severe. When you know exactly what you are allergic to, you are better able to avoid these substances and prevent allergic reactions.

Symptoms of severe allergic reactions can include gastrointestinal symptoms such as stomach cramps, diarrhea, nausea and vomiting. Your respiratory system can also be affected, leading to chest discomfort, difficulty swallowing and breathing and wheezing. Your cardiovascular system reacts with heart palpitations. You become dizzy and lightheaded and your skin becomes flushed and your tongue, face, lips and eyes swell. You may feel weak and lose consciousness.


If you are with someone who is experiencing a severe allergic reaction or anaphylaxis, check his airway, breathing and circulation. If his voice is very hoarse or he can only produce a whisper or coarse vocal sounds, his airway is constricted. He needs CPR and rescue breathing. Calm him down as you are administering first aid. Call emergency medical services. If he has an Epinephrine autoinjector, administer the medication. Have him lie flat and raise his feet about 1 foot and cover him with a blanket.

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