The original plant of Citrus hassaku HORT. Tanaka was found at Jyoudo-Temple in Inno-shima, Hiroshima Prefecture, Japan by Ekei Shounin in the Edo Era. Today, the fresh raw fruits of C. hassaku are cultivated as a seasonal food, and the most famous producing district of the C. hassaku fruit is Wakayama Prefecture, representing about 60% of the Japanese output. The immature fruits of C. hassaku and its three main flavanone glycosides (naringin, neohesperidin and narirutin) have shown inhibitory activities on a compound 48/80-induced histamine release from mast cells, and anti-allergic effects on dinitrofluorobenzen (DNFB)-induced triphasic skin reaction in mice. The contents of the three flavanone glycosides in the immature fruits were higher than those in mature fruits of C. hassaku to skin care for patients with atopitic dermatitis showed improving effects in 76% of the patients. Similar efficacy was obtained for patients with pollinosis.