It could be monosodium glutamate. I understand a large percentage of americans have an allergy to this chemical. It usually causes varying degrees of indigestion and gastrointestinal problems. My fiancee gets quite ill after having chinese food with MSG in it. Took a long time to figure out why. I've heard it said that the allergy can develop over time or build up in your system, apparently MSG isn't quickly removed from the body.