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Green potatoes are regular potatoes that have been exposed to sunlight and as a result have undergone a chemical process that serves to protect them from animals. Chlorophyll pigments are created with the exposure to light and its associated energy. Toxins known as solanine and chaconine are generated as well, which deter animals because the potato will taste bitter. These are also dangerous toxins that affect cell structure and production of a nerve transmitter acetylcholinesterase. The result is often hallucinations and convulsions if the alkaloid toxins are ingested in high enough quantities.
How poisonous green potatoes are directly correlates to how toxic they have become, because the color change and build-up of alkaloids occurs at the same rate. About 15% of the potato crop in the U.S. is discarded due to the potatoes turning green. A study conducted in 2005 by researchers at Washington State University found that the rate of the potatoes turning green was faster than the build-up of poison. The skin of White Rose, Yukon Gold, Dark Red Norland, and Russet Norkotah potatoes had the highest content of toxic compounds, but the levels were not high enough in the flesh to be dangerous.
Each type of potato turned green with light exposure, even if it was at different rates. A grading scale was also developed to calculate the degree of change over a six-day period. The conclusion was that green potatoes might not always have to be thrown out, but it is still important to cut away the green parts if possible. Lower levels of solanine and other potato alkaloids are not immediately dangerous, but there could be toxic effects. These alkaloids also remain in the body for over a day, so eating green potatoes regularly can cause toxins to build up gradually.
Occasional consumption of green potatoes is not dangerous. When potatoes are harvested, they are dug up covered in soil so that they don’t become green. Rain can erode the surface of the soil and expose potatoes, so potato crops can be threatened following a big storm. Sunlight isn’t the only thing that can cause the change, and fluorescent lights in a supermarket can trigger it as well, so it is possible to find green potatoes at the market that didn’t necessarily arrive that way. It is also a good idea to store potatoes away from any light source even after they are brought home.