Food Safety Focus (6th Issue, January 2007) – Incident in Focus

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Food Safety Focus (6th Issue, January 2007) – Incident in Focus

Formaldehyde in Food

Reported by Mr. Arthur YAU, Scientific Officer,
Risk Communication Section, Centre for Food Safety


In the wake of recent public concerns over formaldehyde found in Bombay-duck (a kind of marine fish), this article provides an overview on formaldehyde and discusses its food safety risk.

What is Formaldehyde?

Formaldehyde is a chemical commonly used in industry for the manufacturing of plastic resins that can be used in wood, paper and textile industry. Formalin, which is a solution of about 37% formaldehyde, serves as disinfectant and preservative for household products.

Formaldehyde is ubiquitous in the environment, as it is produced from both natural and manmade sources. It exists at low levels in most living organisms as a metabolic intermediate. Major manmade source of formaldehyde includes combustions (e.g., engine exhaust, wood burning, power plant, waste incineration etc.), building materials and tobacco smoke.

Excluding occupational exposure in industrial settings, major exposure route for formaldehyde in the general population is through inhalation of air, especially indoor air. Formaldehyde can come from recently installed building materials and furnishings. Tobacco smoke can also contribute up to 10 to 25 percent (0.1-1 mg/day) of the exposure from indoor air. Other sources of exposure through gas and dermal contact in the general population include: smog, gas cookers, open fireplace, wood products, textiles, paper, cosmetics and pharmaceuticals etc.

Formaldehyde exists in many animal and plant species as a product of their normal metabolism. Ingestion of a small amount of formaldehyde is unlikely to cause acute effect, but ingestion of a large amount of formaldehyde can generally cause severe abdominal pain, vomiting, coma, renal injury and possible death. However, according to the World Health Organization (WHO), "the general population is exposed to formaldehyde mainly by inhalation."

The main health concern of formaldehyde is its cancer causing ability. The International Agency for Research on Cancer of the WHO classified formaldehyde as "carcinogenic to humans", with consideration that there was sufficient evidence for causing nasopharyngeal cancer in humans, strong but not sufficient evidence between leukaemia and occupational exposure. The WHO, on the other hand, considered that the evidence indicated that formaldehyde was not carcinogenic upon ingestion.

Why Formaldehyde is Present in Food?

As a product of normal metabolism, formaldehyde has been documented to be naturally present in many common food items, including fruits and vegetables, meats, fish, crustacea and dried mushrooms etc., at a wide range of levels (Table 1). In some seafood species, formaldehyde is a natural breakdown product of a chemical known as trimethylamine oxide (TMAO) that exists in their bodies. Trimethylamine oxide breaks down into formaldehyde and dimethylamine in equal parts after the animal dies. The level of formaldehyde can accumulate in certain marine fish during frozen storage and crustacea after death. Its levels were reported to be up to 400 mg/kg in Bombay-duck after cold storage. The detection of dimethylamine in Bombay-duck was used to distinguish whether formaldehyde had been added deliberately.

Table 1: Examples of Foods Known to Contain Naturally Occurring Formaldehyde

Food Type Level (mg/kg)
Fruits and Vegetables Apple 6.3-22.3
Banana 16.3
Cauliflower 26.9
Pear 38.7-60
Shiitake mushroom (dried / raw) 100-406 / 6-54.4
Meat and Meat Products Beef, pork, mutton and poultry meat 2.5-20


Cod 4.6-34
Fish ball 6.8
Crustacean 1-98
Bombay-duck (fresh) ≦140

Since there have been no extensive studies on the levels of naturally occurring formaldehyde in foods, data may not be available for every food. There have been reports of abusive use of formaldehyde in mung bean vermicelli, soya bean sticks and hydrated food (e.g. tripe) previously. Of the over 250 food samples analysed for formaldehyde between 2004 and September 2006, all the results were satisfactory. There is no cause for undue concern over formaldehyde exposure from food so long as you maintain a balanced diet.

s formaldehyde is water soluble, it is recommended, as a good risk reduction measure, that dried food should be thoroughly soaked during preparation (soaking water discarded). Food should also be washed and cooked thoroughly before consumption as a precautionary measure.

Illustration: Examples of food which contain naturally occuring formaldehyde (Top to bottom): fresh shiitake mushrooms and Bombay-duck
Examples of food which contain naturally occuring formaldehyde (Top to bottom): fresh shiitake mushrooms and Bombay-duck

Examples of food which contain naturally occuring formaldehyde (Top to bottom): fresh shiitake mushrooms and Bombay-duck 2

Advice to the Consumers

  1. Wash all food thoroughly with running tap water, as formaldehyde is soluble in water and washing can aid the removal of formaldehyde.
  2. Soak dry groceries like dried mushrooms thoroughly in clean water before cooking and discard the water.
  3. Cook all food thoroughly to an internal temperature of 75°C or above, as heat from cooking can also aid the removal of formaldehyde. For fish, check the flesh to see whether it has turned opaque and can be separated easily.

Advice to the Trade

  1. Source food products from credible sources.
  2. Do not add formaldehyde to food.

Further Information

Readers may obtain further information on formaldehyde in food from the following websites: