What makes a potato unsafe to eat?

December 23, 2025 •

5 min read

As members of the nightshade family, potatoes naturally contain glycoalkaloid compounds, including solanine. This is what makes a potato unsafe to eat when those levels become dangerously high, often triggered by improper storage, light exposure, or physical damage.

Quick Summary

Potatoes can become unsafe due to the buildup of a natural toxin called solanine, indicated by green skin, sprouts, and a bitter taste. Other risks include mold and bacterial growth, such as botulism, which can develop from improper storage or handling of cooked potatoes.

Key Points

Solanine Toxicity: Unsafe potatoes contain high levels of the natural toxin solanine, which can cause gastrointestinal and neurological symptoms if consumed in large quantities.
Green Skin is a Warning Sign: Greening on a potato's skin indicates increased solanine production, triggered by exposure to light. Cut away all green parts, or discard the potato if the greening is widespread.
Sprouts Contain Toxins: The sprouts, or eyes, of a potato have high concentrations of solanine and should always be removed. If the potato is soft and heavily sprouted, it's safer to throw it away.
Mold and Softness Indicate Spoilage: Any signs of mold, foul odor, or a soft, mushy texture mean the potato is spoiled and must be discarded to prevent foodborne illness.
Proper Storage is Key: Store potatoes in a cool, dark, and well-ventilated area, away from other produce like onions, to prevent greening, sprouting, and decay.
Cooked Potato Dangers: Cooked potatoes, especially those baked in foil, can create a low-oxygen environment where botulism bacteria can grow if not cooled properly. Never let them sit out for long.

Understanding the Threat of Solanine Toxicity

While a pantry staple for many, potatoes, like other nightshades, naturally produce toxic compounds called glycoalkaloids to defend themselves from pests and diseases. The most prominent of these is solanine. For healthy potatoes, the concentration of solanine is low and generally harmless. However, under certain conditions, a potato's solanine levels can increase dramatically, posing a significant health risk. Ingesting high levels of solanine can cause a range of symptoms, from mild gastrointestinal issues to more severe neurological problems. This makes identifying and properly handling potentially compromised potatoes a critical part of kitchen safety. Though solanine poisoning is rare, it is a serious concern that is easily preventable with basic knowledge.

What Triggers Increased Solanine?

Several factors can cause a potato's solanine content to rise to unsafe levels:

Light Exposure: When a potato is exposed to sunlight or artificial light, it begins to produce chlorophyll, which causes the skin to turn green. While chlorophyll is not toxic, its presence is a telltale sign that solanine production is also increasing in the same area. The amount of solanine doesn't perfectly correlate with the intensity of the greening, but it serves as a strong warning indicator.
Sprouting: The eyes of a potato, from which new sprouts emerge, are also areas with higher concentrations of solanine and other glycoalkaloids. As the potato ages and begins to sprout, the toxins become more concentrated, especially in the sprouts themselves.
Physical Damage: Any bruises, cuts, or mechanical damage to a potato can trigger the plant's defense mechanisms, leading to an increase in solanine production as a response to injury.
Temperature Stress: Storing potatoes in temperatures that are too cold (like a refrigerator) or too warm can also induce higher levels of glycoalkaloids. Refrigeration, for example, can cause cold-induced sweetening, which is linked to increased acrylamide formation during high-temperature cooking. The optimal storage temperature is between 43–50°F (6–10°C).

Visual and Textural Clues of an Unsafe Potato

Learning to identify the warning signs of a bad potato is the first step in prevention. Beyond the greening caused by light exposure, other physical attributes signal that a potato may be unsafe or past its prime.

Excessive Sprouting: A potato with small, fresh sprouts can often be salvaged by simply removing the eyes and the area around them. However, if the sprouts are long, numerous, and the potato is soft or shriveled, the tuber should be discarded completely.
Soft and Wrinkled Skin: This is a clear sign of dehydration and age. While not directly linked to solanine, a soft potato has lost its moisture and is past its peak freshness. The texture will be compromised, and it's an indicator of impending decay and the risk of bacteria growth.
Mold and Unpleasant Odor: Any visible mold, discolored patches (brown, black, red), or a distinctly foul odor are signs of rotting and bacterial or fungal growth. In this state, the potato is unsafe to eat and should be discarded immediately.

Comparison of Spoiled vs. Salvageable Potatoes

This table provides a quick reference for determining the safety of a potato based on its appearance and condition.


Feature	Salvageable Potato	Unsafe Potato	Recommended Action
Green Skin	Small, localized patches.	Extensive greening throughout the skin.	Cut away all green portions. If greening is deep or extensive, discard.
Sprouts (Eyes)	Small, newly formed sprouts.	Long, multiple, or shriveled sprouts.	Remove small sprouts and cook soon. If numerous or long, discard the whole potato.
Texture	Firm and smooth.	Soft, wrinkled, or mushy.	Cook immediately or store properly. Discard completely.
Odor	Earthy, typical potato smell.	Musty, moldy, or foul odor.	Fine to use. Discard immediately.
Taste	Neutral or sweet.	A bitter, burning taste.	Fine to eat. Discard immediately.

The Botulism Risk with Cooked Potatoes

Another serious food safety concern associated with potatoes arises after they are cooked. Cooked potatoes, especially when wrapped in aluminum foil, create a low-oxygen environment that is ideal for the growth of Clostridium botulinum bacteria. This bacteria produces a toxin that can cause botulism, a severe and potentially fatal form of food poisoning. The risk is highest when baked potatoes are not properly cooled and stored after cooking. To avoid this, it's crucial to:

Remove baked potatoes from foil immediately after cooking.
Store cooked potatoes in the refrigerator promptly, within two hours of cooking.
Never leave foil-wrapped potatoes to cool on the counter for extended periods.

Safe Storage and Handling Practices

Preventing a potato from becoming unsafe starts with proper storage from the moment you bring it home. By controlling its environment, you can significantly reduce the risk of increased solanine and spoilage.

Store in a cool, dark place. A pantry, basement, or cupboard is ideal, as long as it is well-ventilated and kept away from direct light.
Use a breathable container. A mesh bag, paper bag, or open bowl allows for better air circulation and prevents moisture buildup, which can cause rotting.
Keep them separate from other produce. Items like apples and onions release ethylene gas, which can accelerate the sprouting process in potatoes.
Inspect regularly. Check your stored potatoes frequently and remove any that are soft, green, or moldy before they can affect others in the batch.
Do not refrigerate raw potatoes. Cold temperatures can increase the amount of reducing sugars, leading to higher levels of acrylamide when cooked at high heat.

Conclusion: Your Guide to Safe Spud Enjoyment

While potatoes are a beloved and nutritious part of our diet, they require careful handling and storage to remain safe. The primary concern is the natural toxin solanine, which increases with light exposure, sprouting, and physical damage, often signaled by a green tinge on the skin. Other dangers include bacterial growth, particularly the risk of botulism in improperly cooled baked potatoes. By being vigilant about your potatoes' condition and practicing good storage habits—keeping them cool, dark, and separate from other produce—you can minimize risks and enjoy your spuds safely. Always discard potatoes with extensive greening, long sprouts, or signs of mold, and never ignore a bitter taste. For further reading, reliable sources from national food safety organizations provide excellent guidance on safe food handling practices.

Note: This content is for informational purposes only and does not constitute medical advice. Consult a healthcare professional if you suspect you have solanine or botulism poisoning.

Frequently Asked Questions

Yes, if the greening is limited to a small, surface-level patch. Cut away the green portion and at least an eighth of an inch of the flesh beneath it. If the greening is extensive or deep, it's best to discard the entire potato, as the toxin may have spread further.

Eating an unsafe potato, particularly one with high levels of solanine, can lead to symptoms like nausea, vomiting, diarrhea, stomach cramps, and a burning sensation in the mouth or throat. More severe cases may involve headaches, dizziness, or neurological issues.

No, cooking does not effectively destroy solanine. While some methods might reduce it slightly, it is not enough to make a high-solanine potato safe. This is why trimming or discarding the unsafe portions is essential rather than relying on cooking to neutralize the toxin.

Potatoes with small, new sprouts can be safe to eat after you cut the sprouts and surrounding eyes off. However, if the potato is also soft, wrinkled, or has extensive sprouting, it is best to discard it, as the solanine levels are likely high.

Store potatoes in a cool, dark, and well-ventilated space like a pantry or cupboard. Keep them in a paper bag or mesh sack, and away from ripening produce like apples and onions to prevent early sprouting.

Yes, a cooked potato, especially one baked in aluminum foil, can become a breeding ground for Clostridium botulinum bacteria if not cooled and refrigerated promptly. This can cause botulism, a serious form of food poisoning.

If a potato tastes noticeably bitter after cooking, this is a strong indicator of high solanine content. You should not eat it, regardless of its appearance, and discard it to avoid illness.