Food additives, including preservatives, flavor enhancers, and artificial colorings and sweeteners, are found in virtually all processed foods. As a general rule, food additives are unusual causes of food-related symptoms. However, in situations in which no food protein can be identified as the cause of a food reaction, additives should be considered. The additive most commonly implicated in adverse reactions to foods is the family of chemicals called “sulfites.”
Commercially available as sodium and potassium bisulfite, sodium and potassium metabisulfite, and sulfur dioxide, these agents are used to prevent oxidation of foods, including but not limited to white wine, dried fruit, and dried potatoes. They are also applied to fresh foods, such as vegetables in salad bars, fresh seafood, and peeled potatoes, to prevent discoloration. The most common reaction to eating sulfites is the development of acute wheezing in patients with pre-existing asthma.
Rarely, sulfites have been described as causing acute, severe systemic reactions as well.Food dyes, particularly tartrazine (yellow dye no. 5) has been shown to occasionally aggravate chronic hives. This dye is used frequently in foods, such as hard candy, and may also be added to certain medications, including a variety of medicinal syrups (even those used to treat allergy symptoms!). Monosodium glutamate (MSG) is a flavor enhancer used in many prepared foods and was once a common ingredient in Chinese restaurants. Beginning in the 1970s, people reported that MSG caused acute, transient symptoms of headache, disorientation, and occasionally chest pain. However, carefully performed clinical studies have failed to conclusively demonstrate any link between MSG and these symptoms.
In any event, many restaurants no longer add MSG to their freshly cooked foods, making it easier to avoid this additive. Butylated hydroxyanisole (BHA) and butylated hydrox-ytoluene (BHT) are commonly used preservatives that have been suspected of causing hives. However, studies show that these additives are well-tolerated and have not been shown to provoke rashes or any other symptoms. As mentioned earlier, intolerance of these chemicals should be considered in patients with acute reactions to foods. However, definitive confirmation that food additives are the cause of physical symptoms is usually very difficult. Once it can be established that a particular additive was present in a meal that preceded symptoms, it must next be shown that the additive was a plausible cause of the patient’s symptoms.
For instance, sodium metabisulfite would be important in a patient with an attack of asthma but might be much less relevant in a patient with headache. Unfortunately, there are no good laboratory evaluations, such as a blood or skin test, to diagnose a sensitivity to these additives. Therefore, the initial diagnosis may be based upon clinical observations that the additive caused specific symptoms on more than one occasion and that these symptoms did not occur when the additive was avoided. Following these observations, an oral challenge with the additive may be considered to confirm the diagnosis. These challenges are time consuming and technically demanding and require special materials; for these reasons, they are per-formed in specialized centers.