Cranberries may be an effective treatment for the herpes virus, researchers claim.
The berry is known to be effective in treating bladder conditions.
But experts at the Kaohsiung Medical University in Taiwan say in Chemistry and Industry they could also treat the cold sores and genital herpes virus.
However UK experts said there was not enough evidence to suggest people should eat or drink cranberries to treat herpes.
The study is also featured in the Journal of the Science of Food and Agriculture.
The researchers looked at the properties of the Alpine cranberry, a woody-green shrub also known as Vaccinium vitis-idaea.
The plant, also known as lingenberry or partridgeberry, is already used as a treatment for stomach disorders. Its flowers are also dried to produce remedies for lung ailments.
'Not recommending juice'
The Taiwanese researchers isolated a compound called proanthocyanidin A-1.
They examined its effectiveness against herpes virus type 2 (HSV-2 or herpes simplex infection), which causes cold sores and genital herpes.
Laboratory tests showed the compound significantly suppressed HSV-2 infection without any toxic effect.
It did not reduce the infectivity of the virus, but it did reduce its effects.
The team, led by Dr Hua-Yew Chung, suggest proanthocyanidin A-1 prevents the virus attaching itself to cells by disrupting either the glycoproteins around the virus or the host cell membrane.
However, they say further studies are needed to clarify exactly what the mechanism is.
Marian Nicholson, director of the Herpes Viruses Association, told BBC News Online: "This is lab-based research. But I would want to see evidence it works in people before I got excited about its potential."
She added: "In the past, lab tests have suggested that treatments from algae to bleach and a cold hair-dryer could kill the virus.
"So I wouldn't be recommending cranberry juice to people who have the virus."