MSG, or monosodium glutamate, is bad because it seems to stimulate migraine headaches and other unpleasant symptoms in some people. Some food manufacturers don't list MSG on the labels of their foods. That's because MSG occurs naturally in foods such as hydrolyzed vegetable and plant proteins and some flavorings. MSG can also be listed under other names such as L Glutamic acid.
Besides migraine headaches, which are often severely painful headaches on one side of the head, people who react to MSG complain of other problems such as flushing or sweating, chest pain, nausea and weakness. They might also experience heart palpitations, a sensation of tightening in the face or neck or feelings of numbness, burning or tingling. These symptoms, though anecdotal, have come to be known as MSG complex.
The U.S. Food and Drug Administration has deemed MSG to be a safe food additive, and studies that try to determine its dangers to humans have been inconclusive as of 2014. Chinese food is known for containing copious amounts of MSG, but the ingredient is also added to other soups, sauces and luncheon meats. Food manufacturers favor MSG because it adds an umami taste that enhances meaty flavors in food.