From mashed potatoes to crispy fries, the humble potato is a staple in kitchens worldwide, loved for its versatility and comfort-food appeal. However, a concern arises when you encounter a potato with a green hue—should you eat it? 

Potatoes with green spots are more likely to contain elevated levels of the toxin solanine, which can cause digestive symptoms if consumed. However, they could be safe to eat when certain precautions are taken. We spoke with Zachary Cartwright, PhD, lead food scientist at Aqualab and a member of the Institute of Food Technologists Food Safety and Quality Management Division, to find out more. 

Why Do Potatoes Turn Green?

Potatoes—which, of course, grow underground—turn green when exposed to any type of light, whether it’s sunlight, fluorescent lighting in a store, or even the light in your kitchen. The green color is caused by the production of chlorophyll, the same pigment that gives other plants their green color. Chlorophyll itself is harmless and doesn’t affect the potato’s flavor or safety directly. However, the greening process can sometimes indicate something more concerning is happening beneath the surface—an increase in solanine.

What Is Solanine?

Cartwright says solanine is a natural glycoalkaloid poison found in all members of the nightshade family, which includes potatoes, tomatoes, and eggplants. “In plants, solanine serves as a defense mechanism against pests and diseases,” he says. “While potatoes naturally contain small amounts of solanine, the levels increase to toxic levels when the potato is damaged, exposed to light, or stored under too hot or too cold conditions.”

Solanine also causes a bitter flavor. If cooked potatoes taste bitter or cause a burning sensation in your mouth or throat, this can indicate high solanine levels, even if the potato does not look green.

Health Risks of Solanine

Consuming high levels of solanine can lead to solanine poisoning, which, though rare, can cause serious symptoms, including:

• Gastrointestinal distress. Nausea, vomiting, and diarrhea are the most common symptoms associated with solanine poisoning. These symptoms can occur within hours of consuming a green potato.
• Neurological symptoms. In more severe cases, solanine can affect the nervous system, leading to headaches, dizziness, confusion, and even hallucinations.

Most cases of solanine poisoning involve mild symptoms and are often the result of consuming significant amounts of green potatoes, but the only way to completely mitigate the risk is to completely steer clear of any green potato flesh. 

How Much Solanine is Dangerous?

“A potato with solanine levels above 20 milligrams per 100 grams of potato flesh can start to cause symptoms,” says Cartwright, though typical store-bought potatoes usually contain much less than this.

The amount of solanine that can cause poisoning varies depending on several factors, including the individual’s weight, the amount of green potato consumed, and the solanine concentration in the potato. Solanine poisoning symptoms may begin to appear after consuming two to five milligrams of solanine per kilogram of the person’s body weight. For reference, a potato with visible greening might contain around 250 to 280 milligrams of solanine per kilogram, meaning that a small amount of green potato can still pose a risk, especially for children.

What to Do if Your Potato is Green

If you notice a potato has turned green, here are some steps you can take:

1. Assess the greening. If you see green spots on the outside, it doesn’t mean the whole potato is affected. “You can remove the spots and eat the potato,” says Cartwright, “but if it’s too great of an extent, I wouldn’t even mess with that.”
2. Check for sprouts. Green potatoes often develop sprouts, which also contain high levels of solanine. If your potato has sprouted, it’s best to remove the sprouts or discard the potato altogether. If you choose to use the potato, cut or dig the sprouts out completely, removing any green flesh around the sprouts as well.
3. Peel the potato. Since the majority of solanine that’s already present in potatoes is concentrated in the skin and just beneath it, peeling the potato can help reduce the solanine content. Be sure to remove any green flesh as well.
4. After cooking potatoes, be aware of any bitter flavors. Solanine is heat-stable, says Cartwright, meaning that baking, boiling, frying, or cooking the potato in any other way will not reduce its solanine content. Solanine can impart a bitter taste to the potato, so if your potato tastes bitter after cooking, it’s a good indication that it may contain higher levels of solanine and you should stop eating it.

Preventing Potatoes From Turning Green

Commercial potato growers take measures to prevent greening in potatoes from the moment the spuds are harvested to when they arrive on grocery store produce stands. “This includes everything from proper storage and handling to screening measures for greening and sprouting before reaching consumers,” says Cartwright. “This is why you don’t really see green potatoes at the grocery store. But that may change as they sit out on a kitchen counter over time.”

The best way to avoid the risk of solanine poisoning is to prevent your potatoes from turning green in the first place. This comes down to three main factors, according to Cartwright: 

1. Proper storage. Keep potatoes in a cool, dark, and dry place. Reaction with light will cause greening and solanine formation, so this step is key. 
2. Avoid damage. Ensure you’re handling the potatoes carefully to avoid bruising or nicks, which can also cause solanine formation.
3. Consume fresh potatoes. Aging and sprouting will also lead to higher solanine concentrations, so eat your spuds before they sprout or turn green.

The Takeaway: Should You Eat Green Potatoes?

There are potential health risks associated with consuming solanine, a compound present in green potatoes, so it’s best to avoid eating those discolored tubers when you come across them. While small amounts of green potato might not cause severe symptoms, the risks can outweigh the benefits. If you do come across a green potato, your safest bet is to either cut away the affected areas or discard the potato entirely.

By storing potatoes correctly and being vigilant about any signs of greening, you can enjoy this versatile starchy vegetable without worry.