There are many conditions that can mimic food allergy. The possibilities include not only food allergy but also any other diseases that have symptoms brought on by food. These include reactions to certain chemicals in food for example, histamine or food additives, food poisoning, several other gastrointestinal diseases, and psychological symptoms.

Histamine toxicity: Some natural substances (for example, histamine) in foods can cause reactions resembling allergy. Histamine can reach high levels in cheese, some wines, and certain fish, particularly tuna and mackerel. In fish, the histamine is believed to stem from bacterial contamination, especially in fish that has not been refrigerated properly. Histamine toxicity has been referred to as pseudoallergic fish poisoning and accounts for over one-third of seafood-related food-borne illnesses, according to the U.S. Centers for Disease Control and Prevention (CDC).

Food additives: Another type of food intolerance is an adverse reaction to certain compounds that are added to food to enhance taste, provide color, or protect against the growth of microorganisms. Consumption of large amounts of these additives can produce symptoms that mimic the entire range of allergic symptoms.

The compounds most frequently tied to adverse reactions that can be confused with food allergy are yellow dye number 5, monosodium glutamate (MSG), and sulfites. Yellow dye number 5 can cause hives, although rarely. 

Sulfites occur naturally in some foods and wines and are added to others to enhance crispness or prevent the growth of mold. In high concentrations, sulfites can pose problems for people with severe asthma. 

Food poisoning: Eating food that is contaminated with microorganisms, such as bacteria, and their products, such as toxins, is the usual cause of food poisoning. Thus, the ingestion of contaminated eggs, salad, milk, or meat can produce symptoms that mimic food allergy. Common microbes that can cause food poisoning include the noroviruses, Campylobacter jejuni, Salmonella, Listeria monocytogenes, Vibrio vulnificus, and E. coli 0157:H7.

Lactase deficiency (lactose intolerance): Another cause of food intolerance, which often is confused with a food allergy, specifically to milk, is lactase deficiency. This common food intolerance affects at least one out of 10 people. Lactase is an enzyme in the lining of the small intestine. This enzyme digests or breaks down lactose, a complex sugar in milk, to simple sugars, which are then absorbed into the blood. If a person has lactase deficiency, he does not have enough lactase to digest the lactose in most milk products. Instead, other bacteria in the intestine use the undigested lactose, thereby producing gas. Symptoms of lactose intolerance include bloating, abdominal pain, and diarrhea.

Gluten-sensitive enteropathy: Intolerance to gluten occurs in a disease called gluten-sensitive enteropathy, or celiac sprue. Gluten-sensitive enteropathy is caused by a unique abnormal immune response to certain components of gluten, which is a constituent of the cereal grains wheat, rye, and barley. Although sometimes referred to as an allergy to gluten, this immune response involves a branch of the immune system that is different from the one involved in a classical food allergy.

Other gastrointestinal diseases: Several other gastrointestinal diseases produce abdominal symptoms (especially nausea, vomiting, diarrhea, and pain) that are sometimes caused by food. These diseases, therefore, can resemble food allergies. Examples include peptic ulcer, gallstones, non-ulcer dyspepsia (which is a type of indigestion), Crohn's disease (regional enteritis), cancers of the gastrointestinal tract, and a rare condition called eosinophilic gastroenteritis.

Psychological: Some people have a food intolerance that has a psychological origin. In these people, a careful psychiatric evaluation may identify a traumatic event in that person's life, often during childhood, tied to eating a particular food.

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