The National Consumer Affairs Center has found the allergen ginkgolic acid in 12 out of 20 health supplements sold in Japan that use ginkgo tree leaves as a key ingredient.

The allergen could trigger reactions, including skin irritation and gastrointestinal-tract disorders, officials of the center said, noting Ginkgo biloba supplements are sold as food in Japan and there is no law to regulate their ingredients.

In Germany and some other countries, Ginkgo biloba extracts are regulated as medicine and are used to treat poor cerebral blood circulation and other problems.

German health authorities limit the daily intake of ginkgolic acid to less than 0.6 microgram due to potential allergy-causing effects.

By following the instructions printed on the labels of the 20 Ginkgo biloba supplements tested by the National Consumer Affairs Center, a consumer could take up to 48,000 micrograms of ginkgolic acid per day -- 80,000 times the daily intake recommended by German health authorities.

The center said the products made of ground ginkgo leaves showed exceptionally high concentration of ginkgolic acid compared with those made of ginkgo leaf extracts.

"Although there is no law in Japan to regulate Ginkgo biloba products as medicine, any discomfort on consuming the supplements should be immediately reported to a doctor," the center said.

Consumer groups in Japan say they had received 22 complaints up to October related to the consumption of ginkgo biloba supplements other than those tested by the center.

Complaints included rashes, gastrointestinal disorders and respiratory problems.