What foods have formaldehyde in them to avoid and how to reduce exposure

November 14, 2025 •

4 min read

While the human body naturally produces and processes formaldehyde, its presence in some foods, especially through illegal adulteration, is a serious food safety concern. This guide will explain what foods have formaldehyde in them to avoid and how to protect yourself and your family through informed purchasing and preparation methods.

Quick Summary

This article explains the difference between naturally occurring, low-level formaldehyde in foods like fruits and vegetables and harmful, illegally added formalin used for preservation. It identifies high-risk food items and offers practical tips for consumers to minimize exposure, such as proper washing, cooking, and careful sourcing.

Key Points

Natural vs. Added: Low, natural levels of formaldehyde are found in many foods and are safe, while high, illegally added levels pose a serious health risk.
High-Risk Foods: Be cautious with perishable foods like fish and seafood, as well as some hydrated and processed goods like vermicelli, which are susceptible to illegal formalin adulteration.
Smart Shopping: Buy from trusted, reputable retailers and inspect products for unusual stiffness, chemical odor, or unnaturally pristine appearance.
Effective Cooking: Washing produce thoroughly and cooking food completely can significantly reduce formaldehyde levels, as the chemical is water-soluble and volatile.
Diversify Your Diet: Maintaining a balanced diet and avoiding excessive consumption of a narrow range of foods helps prevent concentrated intake of any single chemical.

The Dual Nature of Formaldehyde in Food

Formaldehyde is a simple organic chemical compound that is naturally present at low, safe levels in many living things, including the human body. It is a metabolic intermediate in plants, animals, and microorganisms. However, the problem arises from the illegal use of its synthetic, more concentrated form, formalin, as a food preservative to extend shelf life and improve appearance. Consumers must distinguish between these two sources to make safe food choices. For example, fresh shiitake mushrooms naturally contain high levels, but cooking reduces them significantly. In contrast, a fish illegally preserved with formalin poses a different, more serious risk.

Foods with Notable Naturally Occurring Formaldehyde

Many healthy foods contain trace amounts of formaldehyde as a byproduct of natural metabolic processes. Levels can vary significantly depending on the species, storage conditions, and processing. Cooking can also reduce these levels.

Dried Mushrooms: Dried shiitake mushrooms can contain notably high levels, but proper soaking and cooking can mitigate this.
Fish and Seafood: Certain marine fish and crustaceans, particularly those of the gadoid family like cod and haddock, naturally contain trimethylamine oxide (TMAO), which breaks down into formaldehyde during and after frozen storage.
Fruits and Vegetables: Fruits like apples, pears, bananas, and grapes, as well as vegetables such as cauliflower, kohlrabi, and beetroot, all contain low concentrations of naturally produced formaldehyde.
Instant Coffee: While a trace amount of formaldehyde is in coffee beans, the instant variety can have a higher concentration due to processing.

Foods at Risk of Illegal Formalin Contamination

Illegal adulteration is the primary concern for consumers seeking what foods have formaldehyde in them to avoid. Formalin is a highly toxic, carcinogenic chemical and its use as a food preservative is prohibited in most countries. Some of the most commonly targeted products are perishable goods and certain processed items.

Fish and Seafood: This is one of the most common areas of illegal use, particularly in regions where cold storage infrastructure is limited. The formalin is used to maintain a fresh appearance and texture long after the fish has spoiled.
Hydrated Foods: Products like noodles, vermicelli, dried bean curd, and certain tripe or chicken feet have been found to be illegally preserved with formaldehyde.
Milk Products: Reports have shown higher formaldehyde levels in some commercial milk products compared to pure milk, suggesting potential contamination during processing or preservation to extend shelf life.

How to Spot and Avoid Illegally Added Formaldehyde

Being an informed and vigilant shopper is your best defense against illegal food adulteration. Here are some key signs to watch for:

Abnormal Firmness: Fish or seafood that feel unusually rigid or stiff to the touch, rather than having the natural suppleness of fresh product, may have been treated with formalin.
Lack of Odor: Fresh fish has a distinct “fishy” smell. If the fish has no smell at all or an unnatural, pungent chemical odor, it should be avoided.
Unblemished Appearance: Foods that appear unnaturally pristine, with no signs of normal decay or spoilage, especially in warm conditions, could be a red flag.
Vetting Suppliers: Whenever possible, patronize reliable and trusted food retailers and brands. Direct sourcing from trusted local vendors who can vouch for their handling practices is also a good strategy.

Simple Steps to Reduce Formaldehyde Exposure

Beyond smart shopping, simple at-home preparation techniques can further minimize any potential exposure, whether from natural or illegal sources. Formaldehyde is water-soluble and volatile when heated, making these methods highly effective.

Wash Thoroughly: Rinse all fruits and vegetables under running tap water to help remove any surface chemicals.
Soak Dried Foods: For items like dried mushrooms and vermicelli, soak them in water for 10-15 minutes and discard the water before cooking.
Cook Thoroughly: Heat food, especially meat and fish, to a proper internal temperature. This process helps to vaporize and dissipate any formaldehyde present.
Maintain a Balanced Diet: Avoid consuming excessively large quantities of a single food type. A varied diet reduces the risk of excessive chemical intake from any one source.

Comparison: Naturally Occurring vs. Illegally Added Formaldehyde


Feature	Naturally Occurring Formaldehyde	Illegally Added Formaldehyde (Formalin)
Origin	Metabolic processes in living organisms	Synthetic chemical additive for preservation
Concentration	Typically very low (ppm levels)	Can be significantly higher than natural levels
Health Risk	Generally considered non-toxic at normal dietary levels	High concentrations are toxic and carcinogenic
Mitigation	Reduced by cooking, safe levels in balanced diet	Avoided by smart shopping, visual inspection, and cooking
Presence In	Many fresh fruits, vegetables, meats, fish	Illegally in fish, some processed noodles, hydrated foods

Conclusion

Understanding what foods have formaldehyde in them to avoid involves recognizing the key difference between low, natural levels and dangerous, illegally added chemicals. While trace amounts of formaldehyde are unavoidable in a balanced diet and pose no significant health risk, vigilance is essential when purchasing perishable products that may be targeted for adulteration, such as fish and seafood. By patronizing reliable retailers, inspecting food for signs of freshness, and properly washing and cooking your food, you can effectively minimize your exposure and ensure a safer, healthier diet for you and your family. Remember that the greatest danger comes not from the natural presence of this compound, but from its misuse as a synthetic preservative.

For more information on food preservation chemicals and safety guidelines, consult the Centre for Food Safety(https://www.cfs.gov.hk/english/multimedia/multimedia_pub/multimedia_pub_fsf_06_01.html).

Frequently Asked Questions

Naturally occurring formaldehyde is a low-level metabolic byproduct in many living organisms, generally considered safe. Added formaldehyde (formalin) is a synthetic, more concentrated chemical used illegally as a preservative and is a toxic health concern.

While proper washing and cooking can reduce formaldehyde levels, especially if added, it cannot be guaranteed to remove all of it from heavily contaminated food. It is safer to avoid suspect products entirely.

Dried shiitake mushrooms and certain marine fish like cod, especially after being frozen, can have higher natural concentrations. Proper cooking is recommended for these items.

Suspicious signs include a lack of the typical 'fishy' smell, an unusually stiff or rubbery texture, or an unnaturally fresh appearance despite being displayed for a long time.

Yes, the levels of naturally occurring formaldehyde in fruits and vegetables are very low and well within safe limits. The human body efficiently metabolizes these small amounts.

The main risk comes from chronic, high-level exposure via illegal food adulteration, which has been linked to health issues including damage to internal organs and potential cancer risks.

Since formaldehyde is a volatile compound, thorough cooking and heating can significantly reduce its presence. Washing food beforehand also helps remove any surface residues.