When you reach into a sack of potatoes only to find they’ve started turning green, you’re faced with the conundrum of whether to throw them away.

Some cut their losses and toss the green potatoes, while others remove the green spots and use them anyway.

In fact, the green color and bitter taste that potatoes occasionally develop can indicate the presence of a toxin.

Even so, potatoes with green parts are usually safe to eat when they are prepared properly.

This article covers everything you need to know about green potatoes and whether they pose a risk to your health.

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The greening of potatoes is a natural process.

When potatoes are exposed to light, they begin to produce chlorophyll, the green pigment that gives many plants and algae their color (1).

This causes light-skinned potatoes to change from yellow or light brown to green. This process also occurs in darker-skinned potatoes, though the dark pigments may disguise it.

You can tell whether a dark-colored potato is greening by scratching off part of the skin and checking for any green patches underneath.

Chlorophyll also allows plants to harvest energy from the sun via photosynthesis. Through this process, plants are able to produce carbs and oxygen from sunlight, water, and carbon dioxide.

The chlorophyll that gives some potatoes their green color is completely harmless. In fact, it’s present in many of the plant foods you eat every day.

Nevertheless, greening in potatoes can also signal the production of something less desirable and potentially harmful — a toxic plant compound called solanine (1).

Summary

When potatoes are exposed to light, they produce chlorophyll, a pigment that turns them green. Chlorophyll itself is completely harmless, but it can signal the presence of a toxin.

When exposure to light causes potatoes to produce chlorophyll, it can also encourage the production of certain compounds that protect against damage from insects, bacteria, or fungi (2).

These compounds can be toxic to humans in high doses. However, reports of serious illness are rare.

Glycoalkaloids are the main toxins that potatoes produce. Solanine is a type of glycoalkaloid (3).

Solanine is normally present in low levels in the skin and flesh of potatoes and in higher levels in parts of the potato plant. But when potatoes are damaged or exposed to sunlight, they produce more of it (3).

Greening is a good indicator of the presence of higher levels of solanine in a potato, but it isn’t a perfect measure. This is because the green color is caused by chlorophyll, not solanine.

Although the same conditions encourage the production of both solanine and chlorophyll, they are produced independently of each other (1).

Under the same conditions, different varieties of potato can produce different amounts of solanine. When a high-solanine potato variety is identified, food safety regulators can remove it from the market (2, 3).

Nevertheless, greening is an indicator that solanine may be present. If you find green spots on a potato, peeling the potato and trimming away any sprouts (eyes) or green flesh will usually make it safe to eat.

Solanine also causes a bitter flavor. If cooked potatoes taste bitter or cause a burning sensation in your mouth or throat, this can indicate high solanine levels, even if the potato does not look green (2, 4).

Summary

When exposed to light, potatoes produce a toxin called solanine. In very large amounts, solanine can be harmful to humans. Greening in potatoes is a potential indicator of solanine, but peeling and trimming green areas can remove most of the toxin. Solanine can also cause a bitter flavor in potatoes.

Many countries have rules in place to prevent the sale of potatoes that contain high levels of solanine and other glycoalkaloids.

The Food and Drug Administration limits glycoalkaloids to 200–250 milligrams (mg) per kilogram (kg) of raw potato, or 91–113 mg per pound (lb). Canada has a similar limit of 200 mg per kg (91 mg per lb), while some European countries have a limit of 100 mg per kg (45 mg per lb) (2).

Even with these safeguards in place, potatoes can develop high levels of solanine if they’ve been stored improperly or damaged.

If a potato has developed very high solanine levels, consuming it could potentially make you ill. The risk of illness may be higher for children (2).

Eating large amounts of solanine can cause diarrhea, vomiting, and abdominal pain. A toxic dose is thought to be 1 mg or more of solanine per kilogram of body weight (0.5 mg per lb), though estimates vary (2).

According to the Missouri Poison Center, solanine exposure is low risk. Even after consuming enough solanine to develop symptoms, most people will recover well at home (5).

Extreme cases of solanine poisoning have been reported to cause serious symptoms and sometimes even death. However, these cases are incredibly rare (2).

Overall, potatoes are grown and transported carefully to keep solanine levels low. If you discard green parts of the potato and do not eat bitter-tasting potatoes, you are unlikely to become ill (4).

Summary

Potatoes that contain very high levels of solanine can cause nausea, vomiting, and abdominal pain. Most cases of solanine exposure resolve without treatment.

Solanine levels are highest in the skin of a potato. For this reason, peeling a green potato will significantly reduce its solanine levels (2).

Studies have found that peeling can reduce solanine by 25–75%. You should also remove any sprouts (eyes) and areas of green flesh because they can contain high levels of solanine (2, 4).

In potatoes with very high solanine concentrations, the peeled and trimmed potato might still contain enough to make you sick.

However, cooking the potato — such as by boiling, baking, microwaving, or frying it — can further reduce solanine levels (3).

Solanine has a bitter flavor and can cause a burning feeling in your mouth or throat. If a potato tastes bitter after cooking or causes a burning sensation, do not eat it (2, 4).

In general, if a potato has just a few small green spots, you can cut them out or peel the potato. Because solanine is also produced in higher concentrations around the sprouts (eyes) of a potato, you should remove those as well.

However, if a potato is very green or tastes bitter (an indication of solanine), it’s best to throw it away (6).

Summary

Peeling a green potato and removing any sprouts can significantly reduce its solanine levels. Cooking can also lower the solanine content. It’s best to throw away potatoes if they are very green or have a bitter flavor.

Reports of solanine poisoning are rare. However, it may be underreported because of the generic nature of its symptoms.

Potatoes that contain unacceptable levels of solanine usually do not make it to the grocery store.

Nevertheless, if not handled properly, potatoes can produce solanine after they have been delivered to a supermarket or while being stored in your kitchen.

Therefore, proper potato storage is important for preventing higher levels of solanine from developing.

Physical damage, light exposure, and high or low temperatures are the main factors that stimulate potatoes to produce solanine (2).

Inspect potatoes before purchasing them to make sure they have not been damaged or already started greening.

At home, store potatoes in a cool, dark place such as a pantry, cabinet, or drawer. If you have a root cellar or basement, consider storing them there. Keep them in an opaque sack or paper bag to shield them from light.

Storing them in the refrigerator isn’t ideal, as it’s too cold for potato storage. Some studies have even shown increased solanine levels due to storage at refrigerator temperatures (7).

What’s more, the average kitchen or pantry is too warm for long-term storage.

If you don’t have a cool enough place to store your potatoes, purchase only the amount you plan to use. Store them in an opaque paper bag in the back of a cabinet or drawer, where they will be best protected from light and warmth.

Summary

Potatoes containing high levels of solanine will usually not make it to the grocery store. Still, it’s important to store potatoes properly to prevent them from turning green after you buy them. Store them in a paper bag in a cool, dark place such as a drawer or cupboard.

Green potatoes should be prepared carefully.

Although the green color itself is not harmful, it may indicate the presence of a toxin called solanine.

Peeling and trimming green potatoes can help reduce solanine levels. If a potato is green throughout or your potato dish tastes bitter, it’s best to throw it away.

Inspect potatoes for greening and damage before buying them and store them in a cool, dark place to prevent them from going green before you use them.