MSU Extension Safe Food & Water

What causes potatoes to turn green — and are they safe to eat? 

Light exposure can cause a potato’s skin cells to produce chlorophyll. The chlorophyll then causes the skin to turn green and helps the potato get ready to sprout. Light also activates the skin cells to produce solanine, a glycoalkaloid toxin, which has a bitter taste. 

Throughout this process, a second toxin formed is chaconine. According to Poison.org, the two toxins can cause abdominal pain, diarrhea, vomiting, irregular bowel movements, headache, redness or flushing of the complexion, brain fog, confusion, disorientation and fever. Therefore, you should avoid eating green-skinned potatoes to avoid causing these symptoms.

While few people will eat enough of the bitter-tasting green potato to make themselves sick, Michigan State University Extension still recommends throwing green-skinned and sprouted potatoes away to prevent possible gastrointestinal upset caused by solanine and chaconine. The symptoms are likely to begin within a few hours of eating the green potatoes, but symptoms may sometimes occur a full day or two after eating green potatoes.

When purchasing potatoes from the farmer’s market or grocery store, check them, avoiding any green-colored, shriveled or sprouted potatoes. These are signs of poor quality.

Potatoes must also be stored in a cool, dark, dry location, preferably between 45 and 50 degrees Fahrenheit. The storage location should be well ventilated. With these storage recommendations, the potatoes should remain at their best quality for about a month.

When preparing potatoes for cooking and eating, trim away any small green spots and sprouts or eyes. Do not use green potatoes, trimmed or not, if you have small, young children; they are more susceptible to solanine poisoning due to their small body mass.

An excellent resource with guidelines for how long you can store food is the U.S. Department of Agriculture (USDA) Food Keeper App available online or as a download from your smartphone app store. For best quality and food safety reasons, only purchase enough food that your household will eat in a reasonable amount of time, whether you are storing it in the pantry, freezer, or refrigerator. Use a rotation system called FIFO (first in, first out) in your pantry, so the older products are used up first.

For food safety questions, you can also contact the Michigan State University Extension Food Safety Hotline at 877-643-9882. The hotline is available Monday through Friday, from 9 AM to 5 PM EST.