Fact Check: Potato Greening

Will consuming potatoes with green patches make you sick?

No. Green spots or patches on potatoes (known as “greening”) are just chlorophyll, a harmless compound found in all green plants.¹ At the same time, when a potato turns green, there’s usually an increase in a compound called solanine. If eaten in very large amounts, solanine can cause gastrointestinal symptoms.^1-3 Just to be safe, if you see a green spot on a potato, cut it out and eat the rest. It’s also helpful to store potatoes in a cool, dark place.

FACTS

• Greening occurs naturally in potatoes: Greening can occur any time potatoes are exposed to light—in the field, in storage, on grocery store shelves, or at home. Greening happens due to the formation of chlorophyll, a pigment found in many plant foods including lettuce, spinach, and broccoli. Chlorophyll itself is harmless and tasteless, but in potatoes, chlorophyll formation is associated with formation of glycoalkaloids, most notably solanine. Increased solanine levels can cause potatoes to taste bitter, and if eaten in very high quantities, solanine can cause gastrointestinal symptoms like nausea and vomiting.^1,2
• Only light exposure causes chlorophyll formation, but other factors (including light) can increase glycoalkaloids like solanine in potatoes. These include¹:
  • Bruising, cutting, or slicing during or after harvesting.
  • Processing, particularly if it removes water (e.g., making chips or fries), because it can concentrate the glycoalkaloids.
  • Storage under very hot or very cold conditions or excessive exposure to sunlight.
• Potatoes, as typically eaten, contain little solanine. Breeding programs have produced potatoes with very low levels of solanine for commercial use.² The highest levels of glycoalkaloids are typically found in the sprouts, flowers, leaves, or other actively growing areas of the tuber, which aren’t the parts of potatoes people typically eat.¹ Concentrations of glycoalkaloids are also higher in immature potatoes and decrease as the tuber grows.¹ 
• The FDA sets limits on glycoalkaloids: The FDA considers the maximum acceptable glycoalkaloid content to be 20-25 mg/100 g fresh potato weight (or 200-250 parts per million (ppm). A person would have to consume much more solanine than is ever found in a serving of potatoes for it to be toxic. For example, assuming that a potato contained glycoalkaloids at the advisory level of 200 ppm, a 176-pound person (80 kg) would have to consume over 2 pounds (1 kg) of the affected areas of a potato in a serving to trigger a toxic response. It’s also worth noting that potatoes with this high level of glycoalkaloids would have an unpleasant, bitter, burning taste.⁴
• Minimizing glycoalkaloid formation: Strategies can be employed at harvesting and post-harvesting to reduce glycoalkaloid formation in potatoes.³
  • Harvesting:
    • Keep tubers well covered with soil during growing.
    • Allow tubers to mature before harvest. Avoid harvesting on warm sunny days.
    • Avoid handling methods that cause bruising or physical damage to potatoes.
  • Post-Harvesting:
    • Store in cool, dark place.
    • If you see a spot of green on a potato, cut it out and eat the rest.

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REFERENCES

1. Woolfe JA. The Potato in the Human Diet. Cambridge University Press, Great Brittain. 1987. pp 162-181. https://www.cambridge.org/core/books/potato-in-the-human-diet/28DA6EBB41247F71BE9F576796FAF5DC
2. University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources. Green potatoes: the Problem and the Solution. https://digitalcommons.unl.edu/cgi/viewcontent.cgi?params=/context/extensionhist/article/1089/&path_info=g1437.pdf. Accessed April 4, 2025.
3. Friedman M. Potato glycoalkaloids and metabolites: roles in the plant and in the diet. J Agric Food Chem. 2006; 54:8655-8681. https://pubmed.ncbi.nlm.nih.gov/17090106/
4. Dolan LC, Matulka RA, Burdock GA. Naturally occurring food toxins. Toxins. 2010; 2:2289-2332. https://pubmed.ncbi.nlm.nih.gov/22069686/