Although anyone may develop an allergy at any time in their life, there are risk factors that make some individuals especially susceptible to anaphylaxis. Once an anaphylactic reaction has occurred, it is difficult to predict the severity of subsequent reactions, as some allergies can dissipate over time, whereas others may become more severe.

 
Susceptibility

Anyone can develop an allergy at any time in his or her life, even without specific risk factors. Those at risk for experiencing anaphylaxis include:

• People with a history of allergies¹
• Individuals who have asthma and a food allergy^2,3
• People who have previously experienced anaphylaxis^7,8

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

 
Likelihood and Severity of Repeated Reactions

People frequently outgrow allergies to milk, soybeans, and eggs when they leave childhood, but peanuts, tree nuts, and shellfish allergies tend to be lifelong.^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 they are 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 any particular reaction is thought to depend on:

• The amount of allergen to which a patient is exposed
• The person'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 ancillary factors such as exercise or the co-ingestion of alcohol along with food allergens

In general, however, once a reaction has begun and the more rapidly symptoms appear, it's 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.