Understanding in What Formaldehyde Preservatives Used in Milk Exist

January 9, 2026 •

4 min read

In a 2021 study in Sudan, researchers found formaldehyde in 19.2% of raw milk samples, highlighting the illegal use of this chemical to preserve milk and extend its shelf life. The addition of this highly toxic substance is a serious food safety concern for consumers worldwide.

Quick Summary

Formalin, an aqueous formaldehyde solution, is used illegally as a preservative in milk to prevent spoilage but is highly toxic. It is only legally permissible for analytical preservation of milk samples in controlled lab settings, not for human consumption.

Key Points

Illegal Adulteration: Formalin, an aqueous formaldehyde solution, is illegally added to milk to extend its shelf life by killing spoilage-causing bacteria.
Not for Consumption: Formaldehyde is a toxic and potentially carcinogenic substance that should never be present in milk intended for human consumption.
Legitimate Analytical Use: The only legal use of formalin in the dairy industry is for preserving small milk samples for laboratory analysis, not for sale.
Significant Health Risks: Ingesting formaldehyde can cause severe gastrointestinal issues, and liver and kidney damage.
Detection is Possible: Methods like Hehner's test can detect the illegal presence of formalin, confirming adulteration.
Historical Context: Historically, in the 19th century, some unscrupulous vendors used formaldehyde-based mixtures like 'Preservaline' before regulations were in place.

The Illegal Use of Formalin as a Milk Adulterant

While no legitimate formaldehyde preservatives exist for milk intended for consumption, the substance is used illegally as an adulterant. The primary form used for this fraudulent purpose is formalin, a solution containing about 40% formaldehyde gas in water. Unscrupulous vendors, often lacking proper refrigeration or seeking to extend product life for long-distance transport, add formalin to raw milk. The chemical's potent antiseptic properties kill bacteria, thereby preventing the milk from souring and allowing it to appear fresh for a longer period. However, this practice exposes consumers to a highly hazardous chemical, which can be particularly dangerous for vulnerable populations like children. Food safety regulations in most countries, such as the FSSA in India, strictly prohibit the addition of any preservatives to milk meant for direct consumption.

Why is Formalin so Dangerous?

Formaldehyde is a toxic and potentially carcinogenic substance. When ingested, it can cause a range of serious health issues, including:

Severe gastrointestinal distress, such as vomiting, abdominal pain, and diarrhea.
Damage to vital organs, including the liver and kidneys.
Potential long-term health problems due to its carcinogenic properties.
Potential harm to the central nervous system, including damage to optic nerves.

The Legitimate Use: Preserving Samples for Analytical Purposes

It is crucial to differentiate between illegal adulteration for consumption and the legally sanctioned use of formalin for laboratory analysis. In many dairy industry regulations, a small, carefully controlled amount of formalin is added to milk samples specifically for testing purposes. This preserves the chemical attributes of the milk sample, such as fat content, protein, and total solids, for accurate laboratory analysis over a period of time. This practice prevents the sample from spoiling before it can be tested, ensuring accurate results and fair evaluation of the milk's quality. This preserved sample is never intended for human or animal consumption.

Detecting Formaldehyde in Milk

Detecting the presence of formalin in milk is essential for ensuring public safety. Several chemical tests can be performed to identify this adulterant. A simple and widely recognized method is the Hehner's test.

Common Detection Methods:

Hehner's Test: In this test, a milk sample is mixed with ferric chloride solution and concentrated sulfuric acid. The appearance of a violet ring at the junction of the two layers indicates the presence of formalin.
Chromotropic Acid Test: This method involves mixing a milk sample with a chromotropic acid solution. The development of a yellow-colored solution confirms the presence of formalin.
Rapid Test Kits: Modern, portable test kits are also available for quick and convenient screening of milk samples for formalin and other adulterants.

Comparison: Illegal Adulteration vs. Legal Preservation


Feature	Illegal Food Adulteration	Legal Sample Preservation (Analytical)
Purpose	To fraudulently extend the shelf life of milk for consumption, especially without refrigeration.	To preserve milk samples so their chemical composition can be accurately tested in a laboratory.
Substance	Formalin (approx. 40% formaldehyde) is added directly to milk intended for sale.	A very small, precise quantity of formalin is added to a sealed milk sample.
Quantity	Variable and unknown, posing a major health risk.	Controlled and standardized amount, not for consumption.
Legality	Illegal and punishable under food safety laws.	Legally permitted and standard practice in dairy quality control.
Health Risk	Extremely high; a potential carcinogen and toxic agent.	None, as the sample is disposed of after analysis.

Protecting Yourself from Adulterated Milk

As a consumer, protecting yourself from contaminated milk requires vigilance. The most reliable way is to purchase milk from reputable and trusted brands that adhere to strict quality control standards. Supporting local farmers with transparent practices can also help. For those who suspect milk adulteration, there are simple home tests, like checking for off-odors, but these are not definitive. If you have concerns, report them to local food safety authorities, and if possible, obtain a definitive laboratory test to confirm contamination. Reliable detection requires specialized methods, as detailed in research articles such as those published by the National Institutes of Health (NIH).

Conclusion

Formaldehyde preservatives have no place in consumable milk. While the term 'formaldehyde preservatives' may be associated with milk, the only context where it is legitimately used is for preserving analytical samples in controlled laboratory settings, not for consumer products. The substance, typically in the form of formalin, is a toxic chemical and its presence in market milk is a clear indication of illegal adulteration. Consumers should be aware of this dangerous practice and take steps to protect their health by sourcing milk responsibly and being alert to the signs of adulteration. Regulatory bodies are responsible for enforcing strict laws to eliminate this hazardous practice from the dairy supply chain.

Frequently Asked Questions

No, it is strictly illegal and highly dangerous to use formaldehyde as a preservative in milk for human consumption.

Formalin is a solution of about 40% formaldehyde in water. It is illegally used by some vendors as an adulterant in milk to prevent it from spoiling, making the product appear fresher for longer.

Ingesting formaldehyde is highly toxic and poses serious health risks, including severe digestive problems, damage to the liver and kidneys, and an increased risk of cancer.

A small, controlled amount of formalin is legally used to preserve milk and dairy product samples for analytical testing in laboratories, not for consumption.

Formalin can be detected through various chemical tests, such as the Hehner's test, which produces a violet ring when the contaminant is present.

The best protection is to purchase milk from reputable, regulated brands and to be aware of the signs of adulteration. Suspected cases should be reported to food safety authorities.

Illegal adulteration involves adding formalin to milk for human consumption, while legal analytical preservation is the controlled use of a small amount of formalin in lab samples for testing, with the sample being discarded afterward.