Do all potatoes contain solanine? Unpacking the truth about nightshades

December 20, 2025 •

4 min read

Approximately 78 schoolboys became ill in a 1979 incident in the UK after eating improperly stored potatoes with high glycoalkaloid levels, showing that while a mild toxin, high doses can pose a threat. The key question many home cooks have is: do all potatoes contain solanine, and if so, when should you worry about it?

Quick Summary

All potatoes naturally contain trace amounts of the toxin solanine, a glycoalkaloid that serves as the plant's defense mechanism. The concentration of this compound increases significantly in response to stress factors like light exposure and physical damage. High levels, indicated by green skin and a bitter taste, can cause gastrointestinal and neurological symptoms. Proper storage and preparation are essential for safety.

Key Points

All potatoes contain solanine: The toxin is naturally present in all potato varieties, though typically at harmlessly low levels.
High levels are caused by stress: Solanine concentration increases significantly when potatoes are exposed to light or physical damage.
Green skin is a warning sign: The green color is from harmless chlorophyll, but its presence indicates that solanine levels may also be high, especially near the surface.
Peeling is the most effective method: Since most solanine is concentrated in and directly under the skin, peeling is the best way to remove it.
Cooking doesn't fully eliminate it: Most cooking methods, including boiling, do not significantly reduce solanine levels, especially if the toxin is widespread.
Store potatoes properly: To prevent solanine buildup, store potatoes in a cool, dark, and dry place.
Don't eat bitter-tasting potatoes: A bitter or burning taste is a more reliable indicator of dangerously high solanine levels than greenness alone.
Discard heavily affected potatoes: If a potato is heavily greened or extensively sprouted, it is safest to throw it away entirely.
Children are more susceptible: Due to their lower body weight, children are at a higher risk of solanine poisoning and should not eat green or sprouted potatoes.

Understanding the Natural Toxin in Potatoes

Yes, all potatoes contain solanine, a natural toxic glycoalkaloid. However, the amount is usually so low in a healthy, properly stored potato that it poses no health risk to humans. Solanine is a protective compound produced by plants in the nightshade family, which includes potatoes, tomatoes, and eggplants. It acts as a natural pesticide to ward off insects and fungi. The danger arises when the potato is stressed, causing its solanine levels to increase to potentially harmful concentrations.

The Relationship Between Greening and Solanine

One of the most common signs of a potential problem is a potato turning green. When exposed to light, potatoes produce chlorophyll, which is the green pigment. While chlorophyll itself is harmless, its production is triggered by the same conditions (light exposure) that cause the potato to produce higher levels of solanine. The green color is a visual cue, a warning sign that solanine levels may also be elevated, particularly near the skin. The color change is most obvious in light-skinned varieties, but also occurs in darker potatoes.

Factors That Increase Solanine Content

Several environmental and physical factors can contribute to an increase in a potato's solanine concentration:

Light Exposure: The most significant factor is exposure to sunlight or artificial light during storage. This stimulates the synthesis of both chlorophyll and solanine, especially just under the skin.
Physical Damage: Any kind of damage to the tuber, such as cuts, bruises, or impacts during harvesting and transport, triggers a defensive response that includes increased solanine production at the injury site.
Improper Storage: Storage conditions are critical. Storing potatoes in warm or humid environments can also speed up the process of sprouting and glycoalkaloid accumulation.
Sprouting: Sprouted potatoes have concentrated solanine in their eyes and sprouts. These parts should always be removed.
Fertilization: Some studies have shown that high nitrogen fertilization can increase the glycoalkaloid content in potatoes.

Symptoms and Risks of Solanine Poisoning

Though relatively rare, solanine poisoning can cause unpleasant gastrointestinal and neurological symptoms. Mild cases may be mistaken for gastroenteritis.

Gastrointestinal Symptoms

Nausea and vomiting
Diarrhea
Stomach cramps and abdominal pain
Burning sensation in the throat

Neurological Symptoms

Headaches and dizziness
Fever
Hallucinations (in severe cases)
In more extreme circumstances, paralysis or loss of sensation

Serious poisoning cases are extremely uncommon, partly because the bitter taste of a high-solanine potato is a natural deterrent. However, some fatalities have been documented, particularly among those who are undernourished or in severe cases of mass poisoning incidents. Children are also more susceptible to poisoning due to their smaller body mass.

Comparison of Solanine Reduction Methods


Method	Effectiveness	Mechanism & Notes
Peeling	Highly effective, removing 30–80%	Removes the outer layer where solanine is most concentrated. Peel generously if greening is present.
Deep Frying	Moderately effective, up to 40% reduction	Occurs when temperatures exceed 170°C, the point where solanine begins to degrade. Most other cooking methods are less effective.
Boiling	Minimal effect, only 1-4% reduction	Solanine is heat-stable and boiling does not remove it effectively. Avoid reusing the cooking water.
Trimming	Essential for minor greening	Always cut away all green parts and remove sprouts completely.
Soaking in Water	Variable, can reduce some solanine	A study showed soaking in water or a weak acid (vinegar/citric acid) can reduce solanine by 70-80% when combined with peeling and trimming.

Tips for Safe Potato Handling and Storage

To minimize your risk of elevated solanine levels, follow these best practices for selection, storage, and preparation:

Inspect Before You Buy: Look for firm, blemish-free potatoes without any signs of greening or sprouting.
Store Properly: Keep potatoes in a cool, dark, and dry place with good air circulation, such as a pantry or cabinet. An opaque paper or cloth bag can provide additional protection from light. Avoid refrigeration, as low temperatures can increase solanine content.
Avoid Damaged Tubers: Discard any potatoes that are significantly bruised or damaged.
Remove Green Parts and Sprouts: If a potato has only a small, localized green spot or a few sprouts, you can generously cut away that portion and the eyes before cooking.
Taste Test: If a cooked potato has a bitter flavor or causes a burning sensation, do not eat it. This is a key indicator of high solanine levels.
When in Doubt, Throw it Out: If a potato is very green or heavily sprouted, it's safest to discard the entire tuber. It is not worth the risk of illness. For more comprehensive food safety guidelines, you can consult resources like the USDA's FoodKeeper App.

Conclusion

While all potatoes do contain solanine, the amount in healthy, properly stored tubers is negligible and harmless. The key to safety lies in recognizing the warning signs of elevated solanine, such as green skin and sprouts, which indicate a stress response. By following best practices for storage and preparation—including keeping potatoes in the dark, peeling generously, and never eating bitter-tasting potatoes—you can enjoy this staple food without any risk. The link between greening and high solanine levels is a vital food safety cue that every cook should be aware of.

A note on history

Historically, wild potatoes contained much higher levels of solanine. Centuries of selective breeding have created the modern potato varieties with minimal, safe levels of the toxin, underscoring the importance of proper storage for maintaining that safety.

Sources and Further Reading

Frequently Asked Questions

Solanine is a naturally occurring glycoalkaloid toxin produced by plants in the nightshade family, including potatoes, as a defense mechanism against pests and fungi. Its level is usually harmlessly low in healthy tubers but can increase under stress.

Two primary indicators are visual and taste-based. The most obvious sign is green skin, caused by light exposure that also promotes solanine production. A better indicator is a bitter or burning taste, which directly signals high solanine content.

Yes, peeling is highly effective. The highest concentration of solanine is found in and just beneath the skin, so removing the skin can reduce the toxin by a significant amount.

If the greening is minimal and localized, you can generously cut away the green spots and sprouts to remove most of the toxin. However, if the potato is extensively green or tastes bitter, it's best to discard it entirely.

No, common cooking methods like boiling, baking, and microwaving are largely ineffective at removing solanine. Solanine degrades only at very high temperatures, such as deep frying at 210°C, and even then, only moderately.

Potatoes should be stored in a cool, dark, and dry place with good air circulation. Exposure to light, whether natural or artificial, is the main trigger for increased solanine production.

Symptoms can include nausea, vomiting, diarrhea, stomach cramps, headaches, and dizziness. Severe cases may involve neurological issues like hallucinations, but these are rare.