Oral allergy syndrome (OAS) is defined as the symptoms of IgE-mediated immediate allergy localized in the oral mucosa, and the characteristics depend on the lability of the antigen. Another term used for this syndrome is pollen-food allergy (PFS); the patient is sensitized with pollen via the airways and exhibits an allergic reaction to food antigen with a structural similarity to the pollen (class 2 food allergy). In addition to PFS, latex-fruit syndrome is also well-known as the disease exhibiting OAS. In treating the condition, it must be noted that most but not all symptoms of PFS are those of OAS. In many cases, antigens become edible by heating, but some are resistant to heating. Also, since the exacerbation of atopic dermatitis is occasionally observed after the intake of cooked antigens in asymptomatic individuals, careful inquiry of the history is important in designing the treatment. Immunotherapy against the cross-reacting pollen has also been attempted in PFS.