Anyone can develop an allergy at any time in his or her life, even without specific risk factors. Yet some people, including asthmatics, children, and those with a history of anaphylaxis, have an increased susceptibility to allergic reactions. The likelihood and severity of experiencing a repeat allergic reaction depends largely upon the type of allergen and the individual's sensitivity to it.

Susceptibility

A serious and potentially life-threatening allergic reaction is most likely to occur in people:

• With a history of allergies¹
• Who have asthma and a food allergy^2,3
• Who have previously experienced anaphylaxis^7,8

Children, whose immune systems are immature, are most susceptible to a broad array of food allergies.

The immune system is responsible for guarding the body against perceived invaders, including allergens.

Likelihood and Severity of Repeat Reactions

People frequently outgrow allergies to milk, soybeans, and eggs when they leave childhood, but peanuts, tree nuts, and shellfish tend to be lifelong allergens.^4-6

Sensitivity to insect stings frequently decreases over time or stops altogether, particularly among children. However, according to one study, people who have experienced an allergic reaction to insect venom have a 30% to 60% chance of experiencing a similar or more severe response if stung again.⁷

In fact, it is impossible to predict the severity of future anaphylactic reactions in any particular person. There is no set pattern, but the severity of an allergic reaction is thought to depend on:

• The amount of allergen to which a patient is exposed
• The individual's degree of hypersensitivity to the allergen
  • This can vary according to the health of the patient at the time of exposure and can be exacerbated by other factors such as exercise or co-ingestion of alcohol along with food allergens

In general, once a reaction has begun, and the more rapidly symptoms appears, it is more likely the reaction will be severe.⁸

References

1. Yocum MW, Khan DA. Assessment of patients who have experienced anaphylaxis: a 3-year survey. Mayo Clin Proc. 1994;69:16-23.
    
2. Sampson H, Mendelson L, Rosen J. Fatal and near-fatal anaphylactic reactions to food in children and adolescents. N Engl J Med. 1992;327:380-384.
    
3. Yunginger JW, Sweeney KG, Sturner WQ, et al. Fatal food-induced anaphylaxis. JAMA. 1988;260:1450.
    
4. Wood RA. Anaphylaxis in children. Patient Care. 1997;31(13):161.
    
5. Sampson HA. Food allergy. JAMA. 1997;278:1888-1894.
    
6. Anderson JA. Milk, eggs and peanuts: food allergies in children. Am Fam Physician. 1997;56(5):1365.
    
7. Reisman RE. Natural history of insect sting allergy: relationship of severity of symptoms of initial sting anaphylaxis to re-sting reactions. J Allergy Clin Immunol. 1992;90:335-339.
    
8. Joint Task Force on Practice Parameters, American Academy of Allergy, Asthma and Immunology, American College of Allergy, Asthma & Immunology, and the Joint Council of Allergy, Asthma and Immunology. The diagnosis and management of anaphylaxis. J Allergy Clin Immunol. 1998;101(6 pt 2):S465-S528.