How Fast Can Allergic Reactions Happen?

An allergic reaction can be as mild as a sense of slight itching or as severe as massive swelling that makes it impossible for the person to breathe. Allergies became more common in children in the United States between 1997 and 2011, according to the Centers for Disease Control and Prevention 1. (ref 1) Treatment for allergies can range from observation to medications, and in cases of the most serious reaction -- anaphylaxis -- extensive emergency treatment. Treatment is dictated by the speed and severity of the allergic reaction.

All About Allergies

Respiratory allergy is the most common allergy in children, and 17 percent of children had respiratory allergies in the period between 2009 and 2011, according to the CDC. Less prevalent were skin and food allergies, at 12.5 and 5.1 percent respectively. (ref 1)A June 2007 article in the “Journal of Allergy and Clinical Immunology” noted that 9.1 percent of adults self-reported a food allergy 2. A lower number of adults -- 5.3 percent -- reported a doctor had diagnosed them with a food allergy. (ref 2)Allergic reactions can result from exposure to an inhalant, such as pollen, or to a food, medication, insect venom or substance that comes in contact with the skin 3. (ref 3)

Speedy Reactions

The speed of an allergic reaction can vary, depending on: the person’s sensitivity to the offending substance; the amount ingested, inhaled, injected or spread on the skin; whether the patient had ever been exposed before and how quickly a substance is absorbed. A person who eats a food to which she is allergic, for example, may react more quickly if she has an empty stomach than if the offending food is diluted by the presence of other foods in the stomach. The first time a person is exposed to a substance, she may not have as strong a reaction, because her body has not yet become sensitized. The second and subsequent exposures, however, may result in faster and more severe reactions. (ref 3, 4)

Seconds, Minutes or Hours

Some allergic reactions begin immediately and the patient will begin to react within seconds or minutes of exposure 3. The reaction may be delayed by several hours, however, especially if it is a food. On rare occasions, allergic reactions will not develop for 24 hours or more, according to MedlinePlus 3. (ref 3)The National Institute for Allergy and Infectious Diseases notes that, occasionally, symptoms will go away and recur several hours later 45. The most serious form of allergic reaction, anaphylaxis, can occur within minutes 4. Most of these symptoms result from the release of histamine, a chemical in the body. (ref 4)

Treatment of Allergic Reactions

Treatment for allergic reactions varies according to the cause and severity 3. Lab tests are used to diagnose allergies, but not allergic reactions 3. The diagnosis of an allergic reaction is based on the patient’s symptoms and history of exposure, especially in cases of known allergies. If the reaction is mild to moderate, simple treatments such as reassurance for anxiety and cool compresses or hydrocortisone cream on the itching areas are often beneficial. Over-the-counter antihistamines such as diphenhydramine (Benadryl) may be useful. Some people with severe allergies may also use chewable chlorpheniramine maleate (Chlortrimeton) and self-inject prescription adrenalin (Epinephrine) at the first sign of a reaction. In cases of anaphylaxis, immediate emergency treatment is essential -- dial 911 at the first sign of anaphylaxis. (ref 3, 4,5)