Soy milk allergies typically appear in infants and toddlers, who often outgrow it by age 5, according to the Cleveland Clinic. However, soy milk allergies can develop at any age and last indefinitely. An allergy to soy milk is different than an intolerance. The latter, explains the Food Allergy and Anaphylaxis Network, is a digestive problem with digestive system signs and symptoms, and isn't potentially life-threatening. An allergy to soy milk is an immune system response to the product's proteins, and reactions can be life-threatening.
Skin and Swelling Reactions
Some of the more common signs and symptoms of an allergy to soy milk proteins manifest on the skin. These include itching, hives and eczema breakouts.
The immune system's response to soy milk proteins during an allergic reaction can also cause swelling almost anywhere on the body. However, this sign is usually seen around the face or mouth, including the lips, tongue and throat, as cited by the Mayo Clinic. A tingling sensation may occur in these areas as well.
Gastrointestinal, Respiratory and Other Symptoms
Gastrointestinal symptoms, like those associated with a soy milk intolerance, can also be a sign of an allergy. These include abdominal pain, nausea, vomiting and diarrhea.
An allergic reaction to soy milk proteins can cause various problems with the respiratory system. Wheezing and a runny nose are common lighter symptoms, but more serious signs include tightness in the chest, shortness of breath and difficulty breathing.
Additionally, soy milk protein allergies can cause a lightheaded sensation, dizziness or fainting.
Anaphylaxis
Anaphylaxis is the most serious--and potentially fatal--symptom of an allergic reaction to soy milk proteins. While it's rare, people with asthma or other food allergies are more likely to experience it, according to the Mayo Clinic. Signs include sudden constriction of the airway, swollen throat and difficulty or inability to breathe, inability to swallow and drooling, changes to vocal qualities, accelerated or weak pulse, shock, a sharp drop in blood pressure, widespread flushing, and dizziness or loss of consciousness. Anaphylaxis requires emergency medical treatment.
