Manufacturers started using soy as a substitute for milk back in the 1950s because they considered it less allergenic than cow's milk [source: Wood]. Ironically, soy now has the notorious distinction of being a member of the big eight -- right alongside milk.
Soy allergies are more common among young children than adults; luckily, most children outgrow the allergy [source: Maleki]. Unfortunately, for those who are allergic to it, soy is everywhere. Its high protein content makes it a common additive in packaged foods as well as health foods.
Besides causing standard allergic reactions such as hives, asthma and anaphylactic shock, soy can also cause someone to suffer from colitis, canker sores or an acne breakout.