Green potatoes are not safe to eat in significant quantities. The green color itself isn’t toxic, but it signals that the potato has been exposed to light and has likely accumulated glycoalkaloids, naturally occurring compounds that can cause serious illness at doses above 2 mg per kilogram of body weight. For a 150-pound person, that means roughly 136 mg of total glycoalkaloids could trigger symptoms.
Why Potatoes Turn Green
When potatoes are exposed to light, two things happen at the same time. The tuber produces chlorophyll, which turns the skin and flesh green, and it ramps up production of glycoalkaloids, primarily two compounds called solanine and chaconine. These are the potato’s natural defense chemicals, and they concentrate most heavily in and just beneath the skin.
Blue and red wavelengths of light are the main triggers. Research from Frontiers in Plant Science found that the same light signals that activate chlorophyll production also switch on the genes responsible for glycoalkaloid synthesis. Potatoes kept in complete darkness don’t accumulate either one. This is why the green color works as a rough visual warning: if chlorophyll built up, glycoalkaloids almost certainly did too. The relationship isn’t perfectly proportional, though. Some potato varieties produce more glycoalkaloids than others under the same light conditions, and factors like mechanical damage and high temperatures also raise levels independently of greening.
How Glycoalkaloids Make You Sick
Glycoalkaloids affect the body in two main ways. They inhibit cholinesterase enzymes, which are essential for nerve signaling, and they disrupt cell membranes in the digestive tract. The combination explains why poisoning hits the gut first and can progress to neurological symptoms in more severe cases.
Symptoms are often delayed 8 to 10 hours after eating the potato, which makes it easy to miss the connection. Early signs include abdominal pain, nausea, vomiting, and diarrhea. At higher doses, symptoms can escalate to headache, confusion, hallucinations, dilated pupils, slowed breathing, and in rare cases, paralysis. Lethal poisoning has been reported at estimated doses above 3 mg per kilogram of body weight. Symptoms typically last one to three days.
Fatal cases are extremely rare in modern times, partly because commercial potatoes are bred to stay below safety thresholds and partly because most people find heavily green potatoes bitter and unappetizing. That bitter taste is actually the glycoalkaloids themselves, and it’s a useful second warning after the color.
How Much Green Is Too Much
The unofficial worldwide guideline for commercially sold potatoes is a maximum of 20 mg of total glycoalkaloids per 100 grams of fresh weight. A normal, healthy potato typically contains 2 to 13 mg per 100 grams. A potato that has turned significantly green can exceed that 20 mg threshold several times over, especially in the skin and the layer of flesh just beneath it.
A small green spot on an otherwise normal potato is a different situation than an entirely green tuber. If the greening is limited to a small patch, you can cut away the green area generously (removing a margin of normal-looking flesh around it) and safely eat the rest. If the entire potato is green, or if the flesh beneath the skin is visibly green throughout, it’s best to throw it away. Sprouted potatoes also tend to have elevated glycoalkaloid levels concentrated around the sprout itself, so remove sprouts and the surrounding area before cooking.
Does Cooking Destroy the Toxin
Not reliably. Glycoalkaloids are heat-stable, which means normal cooking temperatures don’t break them down the way they neutralize many other natural toxins. Boiling and microwaving whole potatoes have a negligible effect on glycoalkaloid content. Boiling peeled potatoes does better, reducing levels by about 39%, likely because some of the compounds leach into the cooking water. Frying at typical temperatures (150°C to 180°C) causes little change either. Only frying at very high temperatures around 210°C (410°F) has been shown to reduce glycoalkaloids by roughly 40%.
The most effective step you can take in the kitchen is peeling. Since glycoalkaloids concentrate in and near the skin, peeling a slightly green potato removes a significant portion of the toxic compounds and can bring levels down to a safer range, particularly in smaller, immature tubers where concentrations tend to be higher. But peeling alone won’t make a deeply green potato safe. If the green extends well into the flesh, the glycoalkaloid levels may be too high for peeling to solve the problem.
How to Store Potatoes to Prevent Greening
The simplest way to avoid the problem is to keep potatoes in the dark. Light exposure is the primary driver of both chlorophyll and glycoalkaloid accumulation, so storing potatoes in a paper bag, a closed cupboard, or a dark pantry prevents greening from starting. Avoid plastic bags, which trap moisture and encourage rot.
Temperature matters too. Cool storage (around 45°F to 50°F) slows glycoalkaloid production and sprouting. A standard refrigerator is slightly too cold for ideal potato storage, as temperatures below 40°F convert starches to sugars and affect texture and flavor. A cool, dark basement or closet works well. High temperatures and mechanical damage (drops, cuts, bruising) are additional stress factors that can trigger glycoalkaloid production even without light, so handle potatoes gently and don’t store them near heat sources.
Buy potatoes that look firm and free of green patches at the store, and use them within a few weeks. Potatoes sitting under bright retail lighting have already started accumulating glycoalkaloids before you bring them home.