When potatoes sprout, it means they’ve broken dormancy and started trying to grow into a new plant. The sprouts themselves concentrate natural toxins at levels 20 to 70 times higher than the potato flesh, which is why they deserve your attention. A few small sprouts on an otherwise firm potato don’t necessarily mean you need to toss it, but the situation matters.
Why Potatoes Sprout
A potato is a living tuber designed to reproduce. After harvest, it enters a resting phase where its buds (the “eyes”) stay dormant. Eventually, enzymes inside the potato begin converting stored starch into simple sugars like glucose and fructose, which fuel new growth from those eyes. Warmth, light, and time all accelerate this process. Potatoes stored in a warm kitchen will sprout far sooner than those kept in a cool, dark space.
As sprouting begins, the potato essentially starts feeding its new growth at its own expense. Starch levels drop while sugar levels rise, and the tuber gradually loses moisture and weight. This is why a heavily sprouted potato feels soft and wrinkled: its energy reserves have been redirected into the sprouts.
The Toxin Problem
Potatoes naturally produce glycoalkaloids, primarily two compounds called solanine and chaconine. These act as the plant’s built-in pesticide, protecting against insects and disease. In the white flesh of a normal potato, concentrations are low, typically 12 to 100 mg per kilogram. Sprouts are a different story: they contain 2,000 to 7,300 mg per kilogram. The skin, eyes, and any green patches also carry elevated levels.
Doses of 2 to 5 mg per kilogram of body weight can cause toxic symptoms in humans, and doses of 3 to 6 mg per kilogram can be fatal. For context, a 70 kg (154 lb) person would need to consume a significant amount of sprout material or heavily green potato to reach dangerous levels, but the margin isn’t as wide as you might assume, especially for children or smaller adults.
Symptoms of Glycoalkaloid Poisoning
If someone eats enough of these compounds, symptoms typically appear 1 to 25 hours after the meal, peaking around 4 to 8 hours. The most common signs are nausea, vomiting, diarrhea, and abdominal pain. In more severe cases, people experience headaches, drowsiness, difficulty breathing, and weakness. Gastrointestinal symptoms can persist for 3 to 6 days. Serious poisoning is rare with store-bought potatoes, but it has been documented historically when people ate large quantities of sprouted or green potatoes.
When You Can Still Eat Them
A potato with a few small sprouts is salvageable if the tuber itself is still firm. Cut away the sprouts along with a generous margin of flesh around each eye. Michigan State University Extension puts it simply: as long as the potato is firm and the sprouts are small, you can remove them and safely eat the rest.
Peeling the potato before cooking also helps, since the skin carries higher glycoalkaloid concentrations than the interior flesh. Cooking provides an additional layer of safety. Baking, deep frying, and double frying reduce glycoalkaloid levels in potato peels by 74 to 84 percent. Boiling and steaming are less effective but still cut levels by more than 50 percent. That said, cooking alone shouldn’t be your only line of defense. Remove the problem areas first.
When to Throw Them Out
Toss a potato if it has any combination of these signs:
- Soft or shriveled texture. This means the tuber has lost significant moisture and starch to sprout growth. It won’t taste good, and toxin levels throughout the flesh may be elevated.
- Extensive sprouting. Long, branching sprouts indicate the potato has been actively growing for a while. The more energy diverted to sprouts, the more the potato’s chemistry has shifted.
- Green skin or flesh. Light exposure triggers both chlorophyll production (the green color) and a simultaneous increase in glycoalkaloid production. Research shows potatoes stored under light develop solanine levels roughly 1.6 times higher than those stored in the dark. The green color itself is harmless chlorophyll, but it reliably signals that toxin levels have also risen.
The National Capital Poison Center advises that when in doubt, throw it out. A single potato isn’t worth the risk.
How to Store Potatoes to Prevent Sprouting
Temperature is the biggest factor. Commercial potato storage facilities keep tubers at 2 to 4°C (about 36 to 39°F) with 90 to 95 percent humidity, which prevents sprouting almost entirely. Your refrigerator runs close to this range, though cold storage can convert some starch to sugar and affect flavor and browning during cooking. A cool basement, garage, or pantry in the 7 to 10°C (45 to 50°F) range is a good compromise for home storage.
Keep potatoes in the dark. Light triggers both greening and glycoalkaloid production, so a paper bag, cardboard box, or closed cabinet works well. Avoid plastic bags, which trap moisture and encourage rot.
Store potatoes away from onions, garlic, and fresh fruit. Ripening fruit releases ethylene gas, which signals the potato to break dormancy and sprout. Onions have a similar effect. Give them separate storage spots, and your potatoes will last noticeably longer.