Background: Soy sauce is well-known as a Japanese traditional seasoning, namely shoyu. Usually, shoyu means sauce made from soy. Shoyu does have not only benefits but also adverse effects. Soy sauce allergy which is not caused by soy or wheat allergy is rare.
Patients: Our four patients developed cellulites and dermatitis around lips with irritation after a meal with shoyu. The age of the patients was 10, 35, 46 and 51 years; they were all female.
Objectives: These inflammations can be developed by two causes; first it can be caused by allergic reactions to shoyu; the second, it can be caused by histamine poisoning. It is important to determine whether inflammation is caused by allergic reactions or histamine poisoning.
Methods: We determined the volume of histamine in some sauces and performed prick test and laboratory tests.
Results: Four patients had positive reactions by prick test after using some sauces. We suspected that histamine caused their symptoms, but nine normal volunteers had negative reactions. Patient's specific IgE score to soy and wheat was class 0. The results showed that the sauce made from soybean and broad bean contained histamine, but histamine in other sauces was not detected.
Conclusions: In this study, we confirmed by prick test, four cases of soy sauce allergy, which was caused by some products during brewing. When patients with inflammations around mouth, after a meal containing or using soy sauce, are examined, it should be considered whether dermatitis or cellulites were developed by allergic reaction or by histamine poisoning.