Natural toxins are chemicals produced by living things like plants, fungi, bacteria, algae, and animals. While these toxins don’t hurt the organisms that produce them, consuming food with natural toxins can sometimes be harmful. When suitable preventive measures are not in place, these toxins can enter the food supply, primarily appearing in fruits, mushrooms, and legumes. They also can be in products that contain these foods as ingredients, such as plant-based beverages.

Vegetables, Fruits, Plants and other Foods That Can Contain Toxins

Natural toxins are often produced in plants as a defense against predators, insects, or infestation. Below are some examples of vegetables, fruits, plants, and other foods that can sometimes contain a natural toxin.

Please note that these foods can be safe to eat when properly grown, harvested, and/or prepared. This is not a complete list of all the natural toxins that can occur in food.

• Ackee fruit (Hypoglycin A): Hypoglycin A is a heat stable toxin found in high levels in the rinds and seeds of ackee, a tropical fruit that features prominently in Jamaican cuisine. Reactions to hypoglycin A can range from no symptoms, to vomiting, to coma and death. Properly harvested and prepared ackee will have low levels of hypoglycin and is safe to eat.
• Blue-green algae (Microcystins): Produced by Microcystis and other types of blue-green algae (BGA), microcystins are natural toxins that can cause gastrointestinal distress and potentially damage your liver over time. Microcystis cells can contaminate other BGA used in foods, such as wild-harvested Aphanizomenon flos-aquae (AFA). Properly harvested BGA is safe to eat and is used in some dietary supplements and food products.
• Honey (Grayanotoxins): Bees collect nectar from flowers in order to create honey. If those flowers have a natural toxin, that toxin may end up in the honey from that beehive. One example is grayanotoxins, which plants such as rhododendrons and mountain laurel naturally produce. Eating honey with a high amount of this toxin can lead to “mad honey” poisoning, with symptoms such as nausea, vomiting, or dizziness. This type of poisoning is rare.
• Beans (Phytohaemagglutinin): Phytohaemagglutinin (PHA) is a lectin found in raw or undercooked beans. Lectins are proteins that bind to carbohydrates and some plants produce them as a natural defense mechanism. In canned and properly cooked kidney beans, the low levels of PHA won’t affect you. But at high levels in raw beans, PHA can lead to nausea, severe vomiting, and diarrhea. Soaking the beans for a minimum of 5 hours and then boiling them in fresh water for at least 30 minutes will remove and destroy this toxin.
• Mushrooms (Mushroom toxins): It’s well known that some mushrooms are toxic. Depending on the type of mushroom you eat, you could experience milder reactions like nausea or diarrhea. More severe reactions include coma and death.
• Stone fruit, such as peaches or apricots (Amygdalin): Amygdalin, also called laetrile, is a natural chemical found in the seeds of apricots, bitter almonds, apples, peaches, and plums. The chemical is not found in the fruit itself and accidentally eating a seed or pit will not harm you. However, consuming a large amount of the seeds or pits can be problematic because enzymes in your intestines can turn amygdalin into cyanide and cause cyanide poisoning.

Fish and Shellfish Toxins

Much like with plants, fish and shellfish can contain toxins. When people eat these fish and shellfish, these natural toxins can cause health problems.

Mycotoxins in Foods

Mold or fungus can infect some foods with mycotoxins while the crop is growing or is being stored. Only certain molds and fungi produce mycotoxins that can make you sick if you eat them. Mycotoxins associated with human food include aflatoxins, patulin, fumonisin, ochratoxin A, and deoxynivalenol.

Hypoglycin A is a heat stable toxin that occurs in ackee fruit, a tropical fruit used in Caribbean cuisine. Although native to West Africa, ackee fruit is found in south Florida, Central and South America, and many Caribbean countries.

The edible part of a fully ripe, properly processed ackee fruit is safe to eat. Unripe fruit, and the rind and seeds of ripe fruit, are never safe to eat because they can contain dangerous amounts of hypoglycin A.

People who eat unsafe levels of hypoglycin A may have no symptoms or mild symptoms, such as vomiting. However, others can have severe reactions, such as vomiting with profound hypoglycemia, drowsiness, muscular exhaustion, prostration, and possibly coma and death.

What are the Edible Parts of the Ackee Fruit and When Is It Safe to Eat?

A ripe ackee fruit is about 4 inches long. The rind of the ripe fruit is yellow with an overlay of bright red and three seams. As the fruit ripens, it splits open along the seams into three sections revealing the edible part of the fruit, the fleshy, pale yellow arils. At the top of the arils is a round, black, glossy, hard seed. Between the seed and each aril is a pinkish membrane (raphe).

The amount of hypoglycin A in an ackee fruit often depends on how ripe it is and if it was allowed to ripen naturally. A properly ripened ackee fruit will still have high levels of hypoglycin A in its seed and rind, but low levels in its arils. However, a green unripe ackee fruit has high levels of hypoglycin A in all its parts at roughly 1000 parts per million (ppm). If an ackee fruit has more than 100 parts per million (ppm) hypoglycin A, the FDA considers it to be adulterated and unsafe for people to eat.

How to Reduce the Risk of Hypoglycin A Poisoning from Ackee

Ripe ackee can be frozen, canned, or cooked. Most of the ackee products in the U.S. are imported from tropical countries, such as Jamaica, Belize, and Haiti. If an ackee fruit isn’t properly processed, the finished product might still contain enough hypoglycin A to make it dangerous to eat. Because of this danger, the FDA assesses manufacturers of ackee for export to the United States on a plant-by-plant basis prior to considering the admissibility of their ackee product(s) offered for import into the United States. The manufacturers listed on the “Green List” of FDA’s Import Alert have demonstrated to FDA that they have food safety controls in place to ensure that only properly ripened ackees, without seeds or rind, are included in finished products.

If you are planning to eat ackee, here are some things to keep in mind:

• Do not eat fresh ackee that has not ripened naturally.
• Do not try to cook fresh ackee that has not ripened naturally. Cooking an unripe fruit will not reduce the level of hypoglycin A.
• Do not eat the seeds or rinds of ackee. Ripe ackee fruits still have high levels of hypoglycin A in their seeds and rinds.
• Do not try to prepare raw ackee yourself unless you have been trained to properly handle and process ackee.
• When you are buying canned, frozen, or processed ackee products, you can check if the manufacturer is on the “Green List” of processors in the FDA’s Import Alert.

How Processors Control the Level of Hypoglycin A in Ackee Products

Most processors will buy fruit that is unopened or just beginning to split along the seams. They then typically spread the fruit out on ripening racks to let it finish ripening. Processing staff monitor the fruit, looking for ackee that has split wide open and is ready for processing. If the fruit does not ripen by splitting fully open within three to four days, the fruit is discarded.

When ackee fruit is ripe and splits wide open, there is a dramatic, rapid loss of hypoglycin A in the arils and the raphe. Processors will then remove the black seeds and raphe. Although completely removing the raphe may not always be possible, the amount of hypoglycin A in the raphe is negligible if the fruit has fully ripened.

Problems during processing ackee can result in a finished product with potentially harmful levels of hypoglycin A (more than 100 parts per million). A few examples of processing problems include:

• Employee error in identifying and selecting ackee that is ripe and fully opened
• Heat shocking ackee to make it split open faster rather than allowing it to fully ripen naturally
• Buying ackee that appears ripe, but which may have been opened by the supplier before the fruit fully ripened naturally
• Improper cleaning and washing of the arils

Improperly processed ackee fruit can pose a health risk to anyone who eats it.

Generally, eating fully cooked food that is served hot helps you avoid foodborne disease, sometimes called food poisoning. However, there are a few types of foodborne diseases you can get from fish that cannot be prevented by cooking.

During travel if you think you have food poisoning from seafood seek medical care immediately.

Shellfish Poisoning

There are several types of toxins in contaminated shellfish that can cause illness. Toxins may be in found in mussels, oysters, clams, scallops, cockles, abalone, whelks, moon snails, Dungeness crab, shrimp, and lobster.

Shellfish usually become contaminated during or after algae blooms. Shellfish poisoning symptoms differ in severity and depend on the type of toxin in the shellfish. If you’ve recently eaten shellfish and develop the following symptoms, seek medical care.

Symptoms

Symptoms usually appear 30–60 minutes after eating contaminated shellfish, but it could be a few hours before you start to feel sick. Severe cases may be fatal. Symptoms vary based on the type of toxin in the shellfish and can include:

• Numbness and tingling
• Headache
• Nausea
• Vomiting
• Diarrhea
• Confusion

Prevention

Avoid potentially contaminated shellfish. If you’re visiting an area that’s recently experienced an algae bloom, sometimes called “red tide” or “brown tide,” avoid eating shellfish. You may want to avoid shellfish completely if you are traveling in a low-income country or if you aren’t confident of the water quality where the shellfish are from.

Ciguatera

You can get ciguatera (sig-wah-TARE-ah) poisoning by eating fish contaminated with toxins produced by tiny algae found around coral reefs. It can be difficult to tell if fish is contaminated as the toxins that cause ciguatera do not change the appearance, taste, or smell of the fish. Cooking does not destroy the toxins.

Ciguateria can accumulate in reef fish that eat other fish. Fish you may want to avoid include barracuda, moray eel, grouper, amberjack, sea bass, sturgeon, parrot fish, surgeonfish, and red snapper.

Signs and Symptoms

Ciguatera symptoms usually develop 3–6 hours after eating contaminated fish but may start up to 30 hours later. If you’ve recently eaten fish and develop symptoms, seek medical care.

Common symptoms include:

• Nausea
• Vomiting
• Diarrhea
• Stomach pain

Less common symptoms can include:

• Tingling
• Tooth pain or feeling as if teeth are loose
• Itching
• Metallic taste in the mouth
• Blurred vision
• Increased sensitivity to hot and cold

Symptoms usually last a few days but, in some cases, can linger for months. There is no cure for ciguatera, however there are treatments for some of the symptoms. After recovering you may want to avoid fish, nuts, alcohol, and caffeine for at least 6 months to prevent symptoms from returning.

Prevention

Avoid or limit eating fresh reef fish, especially barracuda and moray eel, as they are more likely to cause ciguatera. Do not eat the fish’s liver, intestines, eggs, or head because they have the highest concentration of toxins.

Scombroid

Scombroid (SKOM-broyd) poisoning is caused by eating fish that has not been properly refrigerated after being caught.

Scombroid occurs worldwide and is one of most common fish poisonings. Scombroid poisoning can occur from eating tuna, mackerel, mahi-mahi (dolphin fish), sardines, anchovies, herring, bluefish, amberjack, and marlin.

Signs and Symptoms

Scombroid symptoms usually develop within a few minutes to an hour after eating contaminated fish. They often resemble an allergic reaction and may include the following:

• Flushing of the face
• Headache
• Heart palpitations (fast-beating, fluttering, or pounding heart)
• Itching
• Blurred vision
• Cramps
• Diarrhea

Symptoms can be treated with antihistamines. Even without treatment, people usually get better within 12–48 hours

Prevention

The best way to avoid scombroid is to only eat fish that you know has been properly stored. Contaminated fish usually look and taste normal, but may taste peppery, sharp, or salty. Keep in mind that cooking, smoking, or freezing the fish does not prevent scombroid.

Blue-green algae are a unique type of bacteria, also known as cyanobacteria, that grow in water. Certain blue-green algae grown in freshwater lakes and aquaculture ponds are used in dietary supplements and as an ingredient or color additive in other foods. One commonly used type is AFA (Aphanizomenon flos-aquae), which is wild harvested from Upper Klamath Lake in Oregon.

Other types of cyanobacteria, such as Microcystis species, can sometimes grow in the same lake as AFA. These cyanobacteria produce natural toxins called microcystins, which can present health risks. If companies do not test for microcystins, the AFA they harvest could inadvertently be contaminated with these toxins.

Health risks

If present at significant levels, microcystins can cause liver and kidney damage when consumed. Microcystins have also been shown to cause tumors in laboratory animals. 

Microcystins can affect your health differently depending on how you are exposed (whether through swimming or something you ate), how much you are exposed to, and how often you are exposed. The effects of low-level, long-term exposure to these toxins for any route of exposure is still being determined. For more information on the health effects of exposure to microcystins from the environment (such as from swimming), please see the Microcystin Exposure from Cyanobacterial Harmful Algal Blooms box below.

Recommendations

If you consume products with added AFA or other blue-green algae, here are some steps you can take:

Be an informed consumer. As with all food and drinks you consume, you can stay informed and help others by doing the following:

• Check for recall alerts from the FDA. Our Recalls, Market Withdrawals, & Safety Alerts page lists all current recalls. You can also sign up on that page to receive recall alerts.
• Report adverse reactions. If you have any kind of reaction to or complaint about a blue-green algae product that is a dietary supplement or other food, you can report it to the FDA. You can also see the database of complaints in our CFSAN Adverse Event Reporting System (CAERS).

Learn from the label. If you want to know if a product you consume contains blue-green algae, check the label. Manufacturers of dietary supplements and other food products are required to list ingredients on their product labels. For example, the ingredient section may say “blue-green algae” or “Aphanizomenon flos-aquae” to specify the type. You can learn more on our Food Labeling & Nutrition page.

Follow the directions for use on the label. For dietary supplements, labels include the serving size and the amount of blue-green algae per serving. Don’t take more than this amount. 

Check with your healthcare provider before buying or using a supplement, especially if you are pregnant, nursing, or have a chronic medical condition. Also, check with your pediatrician before giving children dietary supplements. A dietary supplement sold for adults may not be appropriate for children to consume. Also, a recommended serving size for adults may not be a safe amount for children because their bodies are smaller. Most of the blue-green algae products we tested in 2016 were recommended for adult use only, but several labels also contained recommended amounts for children under 12. Checking with your pediatrician first is always a good choice.

Some foods—such as grains, dried beans, dried fruits, and coffee—are susceptible to fungus or mold that produce toxins known as mycotoxins. Only certain molds and fungi can produce mycotoxins of concern. If you eat something containing high levels of those mycotoxins, you can get sick. If you eat something from an animal that ate mycotoxins (such as milk from a cow that ate mycotoxin-infected corn), you can get sick.

As an individual consumer, you generally cannot control the presence of mycotoxins in your food. The fungi that produce mycotoxins generally grow during crop production and storage – steps in the food supply chain that the FDA regulates and monitors to ensure the food available for you to buy is not contaminated. The mycotoxins in human food that the FDA currently focuses on are aflatoxins, deoxynivalenol, fumonisins, patulin, and ochratoxin A.

Aflatoxins

Aflatoxins are mycotoxins produced by certain Aspergillus molds. Several types of aflatoxins exist, but food contamination usually involves aflatoxins B1, B2, G1, and G2 for crops and M1 for milk.

Environmental factors such as temperature, humidity, and the amount of rain affect whether mold will grow on food while it is growing, being harvested, and/or stored. The foods most susceptible to aflatoxins include peanuts, corn, tree nuts such as Brazil nuts and pistachios, and some small grains such as rice. Aflatoxin M1 is also found in milk of cows that eat aflatoxin B1 contaminated crops.

Regularly eating foods with aflatoxins can increase your risk of liver cancer, cause birth defects, and lead to kidney and immune system problems. Eating food containing a large amount of aflatoxins at one time can lead to liver failure and even death.

Because of these health risks, the FDA has published action levels for aflatoxin and regularly tests foods for the presence of aflatoxins. By using modern agricultural and processing techniques, companies can reduce the possibility of contamination in their products.

Deoxynivalenol

Several Fusarium molds produce deoxynivalenol (DON), also known as vomitoxin. The mold grows on wheat, corn, oats, barley, and other grains under normal weather conditions, but especially in cool, wet conditions.

Processing wheat properly can reduce the level of DON in products like flour but will not completely get rid of it. The FDA has published an advisory level for DON in finished wheat products (like flour) that humans eat. When the amount of DON in a food product is at or lower than the FDA advisory level, it does not appear to pose a danger to people who eat these food products.

DON has been found in bread, noodles, beer, popcorn, and other foods. Eating foods with high levels of DON can cause vomiting, nausea, and other symptoms.

Fumonisins

Certain strains of the Fusarium molds produce mycotoxins called fumonisins. These molds commonly infect corn but also sometimes infect other grains like wheat.

The level of fumonisins in a corn product depends on weather conditions. High levels of this toxin occur when hot, dry weather is followed by a period of high humidity. Milling, storage, and manufacturing processes can also affect levels of contamination with fumonisins.

We know that fumonisins can cause a variety of illnesses in animals, especially to their liver and kidneys, but more research is needed to know exactly how these toxins affect humans. The FDA has published guidance levels for fumonisins.

Patulin

Patulin is a mycotoxin produced by Penicillium, Aspergillus and Byssochylamys molds that grow on fruit, grains, and cheese. The best-known example is patulin in juice or cider made from apples. Good harvest and storage practices—such as removing rotten portions of fruit—can get rid of or greatly reduce patulin contamination. Fermentation also appears to destroy patulin so it is not typically found in vinegar or alcohol made from fruit susceptible to the molds.

The risk of patulin contamination increases when companies use moldy apples to make apple juice. Pasteurization won’t get rid of patulin. Drinking the contaminated apple juice can cause nausea, vomiting, and possibly damage the DNA in some body cells.

The FDA has set an action level for patulin in apple juice and apple juice products.

Ochratoxin A

Ochratoxin A is a mycotoxin produced by certain Aspergillus and Penicillium molds. It’s been found in contaminated grains, such as wheat, rye, oat, and barley, and in coffee, grapes and wine. Contamination generally occurs when these foods are not stored and/or dried properly.

We know that ochratoxin A can cause kidney damage in animals. It may possibly cause cancer in humans, but more research is needed to know exactly how this toxin affects humans.