With two more deaths reported Thursday, a total of four people have died after taking a supplement containing beni kōji (red fermented rice) made by Kobayashi Pharmaceutical, with about 93 hospitalized.

The Osaka-based company and the health ministry are scrambling to find answers as the cause of the death remains unknown. Kobayashi Pharmaceutical, along with other companies who use beni kōji in their products, are issuing voluntary recalls as public concern grows over the substance.

However, experts say that there are no dangers in the beni kōji itself and that the health hazard was most likely caused by some unknown substance that made its way into batches of the supplement produced during a certain time frame.