Timing Matters in a Delayed Allergic Reaction

Timing is everything when it comes to suffering a serious allergic reaction.

Until recently, most doctors believed that an anaphylactic response always occurred within minutes of exposure to an allergen. But now some experts from the medical community have discovered that for a small group of people, the window for experiencing an allergic response can be much wider than expected.

Discovery of a Delayed Allergic Reaction

Scientists from the University of Virginia have discovered a new phenomenon called "delayed anaphylactic reaction" or "delayed anaphylaxis." This condition, which can occur between three and six hours after exposure to an allergen, doesn't seem to be widespread. It only affects people with certain blood types, including A and O, who have recently been bitten by a common tick. (People with other blood types seem to be immune to the problem.) The tick bite seems to kick-start the allergy process by changing the way a person's immune system responds to red meats such as beef and lamb.

Symptoms of Delayed Anaphylaxis

The symptoms of a delayed allergic reaction are usually progressive, starting with itching, then moving into hives, swelling, and intestinal distress. In some cases, swelling of the airways and difficulty breathing, rapid heart rate, and a drop in blood pressure can also occur, and can even be life threatening. 

The findings, reported in The Journal of Allergy and Clinical Immunology in 2008, reveal that the way red meat triggers a delayed allergic reaction is different from what scientists have always expected. In regular allergic reactions, the body responds to the protein contained in the allergen. But with delayed anaphylaxis, the response seems to be triggered by the sugar, or alpha gals, that are contained in the meat. This finding sheds new light on the allergic reaction process and as such, may help to shape future treatment options.

How to Avoid a Delayed Allergic Reaction

If you have type A or O blood and are worried about your risk for delayed anaphylaxis, just knowing it exists is an important first step. You should always try to avoid being bitten by a tick, regardless of your blood type. The best way to protect yourself is to wear long sleeves and pants when hiking or traveling in wooded areas. It's also a good idea to use insect repellent as an extra precaution. After spending time outside, check yourself carefully for ticks and if you do find any and could be vulnerable to a delayed allergic reaction, be sure to call your doctor for advice.

If in doubt, you may want to swear off red meat and stick to eating chicken and fish for a while. You should also ask your doctor if it's necessary to carry an EpiPen® in case of an emergency. If you do notice any unusual symptoms, always seek medical treatment immediately.




Commins, SP, et al. "JACI Highlights - December 2008: Delayed Anaphylaxis, Angioedema or Urticaria After Consumption of Red Meat in Patients with IgE Antibodies Specific for Galactose-α-,3-Galactose (alpha-gal)." American Academy of Allergy, Asthma, and Immunology. AAAAI, Dec. 2008. Web. 19 May 2011.

Commins SP, et al "Testing for IgE Antibody to the Carbohydrate Galactose-a-1,3- Galactose (alpha-gal) in Patients with Recurrent, Idiopathic Anaphylaxis: How Many Cases are We Missing?" American Academy of Allergy, Asthma, and Immunology. AAAAI, 2010. Web. 19 May 2011.

"Study describes "delayed anaphylaxis," a new notion in diagnosing food allergies." University of Virginia Health System. Healthsystem.virginia.edu. May 14 2009. Web. 19 May 2011.