Potatoes are a staple food, but signs like green patches, soft spots, or sprouts often cause concern about safety. When a potato shows these signs, its chemistry has changed, making it potentially harmful to consume. This change signals that the potato has been stressed, triggering a significant increase in naturally occurring toxins. Eating potatoes in this condition, even after cooking, can lead to adverse health effects ranging from mild stomach upset to severe poisoning.
The Hidden Danger: Understanding Glycoalkaloids
The danger in a compromised potato comes from compounds called glycoalkaloids, primarily alpha-solanine and alpha-chaconine. These substances are naturally produced by the potato plant as a defense mechanism. While present in low, safe concentrations in healthy tubers, their levels increase dramatically when the potato is exposed to light, physical damage, or warm temperatures that prompt sprouting.
The green coloring on the skin is chlorophyll, which is not toxic itself, but serves as a visual warning. Chlorophyll production and glycoalkaloid synthesis are both activated by light exposure, making green areas a strong indicator of elevated toxin levels. The highest concentrations are found in the green skin, the sprouts, and the “eyes” of the potato. A concentration exceeding 200 milligrams per kilogram of fresh potato is considered unsafe for human consumption.
Immediate and Severe Symptoms of Poisoning
Ingesting potatoes with high levels of glycoalkaloids can lead to acute poisoning, with symptoms typically appearing 30 minutes to 12 hours after consumption. The first signs of illness usually involve the digestive system.
Gastrointestinal Symptoms
Gastrointestinal symptoms include nausea, vomiting, abdominal pain, stomach cramps, and diarrhea. These effects are often coupled with a distinct bitter taste or a burning sensation in the mouth and throat, which serves as an early warning. Mild cases may only result in stomach discomfort that resolves within a day. The severity of the reaction depends on the total amount of toxins ingested relative to a person’s body weight.
Neurological Symptoms
More severe poisoning affects the nervous system. Neurological symptoms can include headaches, fever, confusion, dizziness, drowsiness, apathy, restlessness, and shaking. Extreme exposure can lead to vision disturbances, a low body temperature, and a weakened pulse. The most dangerous effects involve compromised motor function, such as paralysis, and depression of the respiratory and cardiovascular systems, which can result in shock, coma, or, very rarely, death. Hospitalization may be necessary for severe and persistent symptoms.
Prevention and Safe Handling Practices
Protecting potatoes from conditions that raise glycoalkaloid levels is the primary way to prevent poisoning. Proper storage involves keeping potatoes in a cool, dark, and dry environment to minimize light exposure and inhibit sprouting. Ideal home storage conditions are typically between 41°F and 46°F, which slows the rate of sprouting.
Store potatoes in a breathable container, such as a paper bag, and keep them away from produce like apples and onions, which accelerate sprouting. If a potato has only minor greening or a few sprouts, it may be possible to salvage it.
All sprouts must be completely removed, and any green or bruised sections should be cut away generously, as toxin concentration is highest there. If the potato shows extensive greening, is soft, shriveled, or has a noticeably bitter taste, discard it entirely. Since cooking does not eliminate the toxins, removing the affected parts before preparation is the only effective way to reduce the risk. Peeling the potato before cooking can also significantly reduce the total glycoalkaloid content.
When to Seek Medical Attention
While mild gastrointestinal distress may pass quickly, certain signs require immediate professional medical evaluation. Seek emergency care if symptoms are severe and persistent, or if the affected person is unable to keep fluids down.
Red flag symptoms indicating a serious reaction include disorientation, delirium, confusion, a significantly slowed pulse, difficulty breathing, or vision changes. If a person, especially a child, has ingested a noticeably green or sprouted potato and is showing more than minor stomach upset, contact poison control immediately. Providing the person’s age, weight, and the estimated amount and time of ingestion will help emergency services determine the appropriate course of action.