Why can ackee be poisonous when it is not harvested at the proper stage?

The ackee fruit (Blighia sapida), a member of the soapberry family (Sapindaceae), is only safe to consume when it has reached the proper stage of maturity.

The fruit is poisonous when immature or overripe because it contains toxins that can be fatal if ingested. Specifically, the arils—the edible, fleshy white or yellowish portions of the fruit—are attached to the seeds by a toxic pink raphe. When the fruit is unripe, these toxins are present in the arils in dangerous concentrations.123

For safe consumption, one must wait until the reddish woody shell of the fruit has naturally split open at maturity, revealing the arils. It is essential to adhere to these harvesting practices to avoid the severe health risks associated with consuming the fruit at an improper stage of development.123