Soy allergy affects 0.5 percent of children, and the median age at which the problem becomes apparent is 3 months. It is less common than cow's milk allergy, which affects up to 7.5 percent of children, and generally resolves before adulthood. Soy is ranked as the eleventh most allergenic food.
Causes
Soy allergy occurs when an infant's immune system mistakenly identifies proteins found in soy formula as a threat. The child's body produces antibodies called immunoglobulin E or IgE in response, and the next time she is exposed to soy, the IgE antibodies trigger a cascade of inflammatory immune responses. This immune response and subsequent inflammation results in an allergic reaction, which may be mild or severe. The most severe reactions, though rare, may be life-threatening.
Symptoms
The most frequent symptom of soy allergy in newborns is diarrhea. Other signs of a problem include vomiting, crabbiness, skin irritation and runny nose. Fortunately, the potentially life-threatening allergic reaction called anaphylaxis is rare in infants, but signs include swelling of the face and neck that may cut off the airway, along with rapid pulse, low blood pressure and fainting. If you suspect anaphylaxis, call 911 immediately. Otherwise, make an appointment with your pediatrician or an allergist.
Diagnosis
Your doctor will want to know if your baby's symptoms appeared soon after changing to a new formula containing soy, and he may also ask if you have previously breastfed. Bring labels from the soy formula or any other recently introduced foods to the appointment and be prepared to answer questions about your family history of allergy and asthma. There are two clinical tests for soy allergy; one is a skin-prick test, and the other is a blood test performed at a lab.
Treatment
The only treatment for soy allergy is avoidance. Switch to a soy-free infant formula and avoid soy when introducing your baby to solid foods. Unfortunately, the second task can be unexpectedly challenging, since many processed foods use soy products as additives and fillers. Commonly used soy products include hydrolyzed vegetable protein, textured vegetable protein, tempeh, tofu, lecithin, miso, yuba, okara, nato, tamari, teriyaki and shoyu. Always check product allergy listings. Call the manufacturer if you are unsure about something.
References
- Illinois College of Agricultural, Consumer & Environmental Services; Soy Allergy; Clare M. Hasle
- Mayo Clinic; Soy Allergy Causes; May 2011
- Mayo Clinic; Soy Allergy Symptoms; May 2011
- Mayo Clinic; Soy Allergy - Preparing for Your Appointment; May 2011
- Mayo Clinic; Soy Allergy Tests and Diagnosis; May 2011
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