THIOUREA--PROHIBITED

CAS: 62-56-6 ANTIMICROBIAL AGENT

Thiourea (CAS 62-56-6) is a small organosulfur chemical historically studied for various industrial uses; in the context of food regulation it is specifically listed as a prohibited substance under US FDA food additive regulations.

What It Is

Thiourea is a synthetic organosulfur compound with the molecular formula CH4N2S that is known from industrial settings rather than food production. It is not a food additive in jurisdictions where it has been evaluated and is instead listed in regulatory texts as prohibited for direct addition to human food; this means it must not be intentionally added as an antimicrobial agent or for any other purpose in food products. Other synonyms include thiocarbamide and several alternate systematic names reflecting its chemical structure. The CAS registry number 62-56-6 uniquely identifies this compound in chemical and regulatory databases. Across regulatory inventories, it appears not because it is permitted but because authorities explicitly restrict its use in foods on safety and lack-of-evidence grounds.

How It Is Made

Thiourea is typically synthesized through classical chemical processes in laboratory or industrial reactors. One common route begins with the reaction of ammonium thiocyanate under controlled heating conditions, often producing thiourea by rearrangement. Alternative preparative routes involve the combination of cyanamide with hydrogen sulfide under elevated temperature and pressure to yield the thiourea compound. In all of these processes, standard purification techniques such as recrystallization are used to isolate solid thiourea from the reaction mixture. These chemical synthesis methods reflect general preparative chemistry rather than food-grade manufacturing, because thiourea is not used as a food ingredient.

Why It Is Used In Food

Intentionally, thiourea is not used in food because food safety regulators have determined that it should be excluded from direct addition based on potential risks and lack of safety data supporting its use. Historically, it was evaluated for possible antimicrobial or antimycotic uses, such as treatment of agricultural crops, but rigorous food safety evaluation did not support its inclusion as a food additive. Regulatory lists of substances prohibited from direct addition to human food include thiourea specifically, indicating that any food containing detectable levels of this substance is considered adulterated and unsafe for human consumption under applicable laws.

Adi Example Calculation

An illustrative ADI calculation typically involves multiplying a no-observed-adverse-effect level (NOAEL) from toxicology studies by a safety factor to account for uncertainties, yielding a conservative intake level protective of public health. However, because thiourea is not an authorized additive and lacks an established NOAEL or approved ADI from food regulatory authorities, there is no numerical example that regulators use for dietary intake. This absence highlights the distinction between permitted additives with ADIs and prohibited substances, where no safe dietary concentration has been defined.

Safety And Health Research

The scientific literature and safety data sheets on thiourea highlight that this compound presents hazards typical of many industrial chemicals, including concerns about acute and chronic toxicity. Laboratory toxicity studies indicate effects including irritant and systemic toxicity in animal models, and thiourea is classified in some hazard systems as having carcinogenic and reproductive toxicity potential. These findings form part of the basis for regulatory exclusion from food use. The absence of a demonstrated safe exposure level for humans via the diet and evidence of adverse effects in toxicological studies inform regulatory decisions to prohibit its addition to foods rather than permitting it under controlled conditions.

Regulatory Status Worldwide

In the United States, thiourea is explicitly listed in the Code of Federal Regulations at 21 CFR 189.190 as a substance prohibited from direct addition to human food, meaning any added or detectable level in food renders the product adulterated under the Food, Drug, and Cosmetic Act. This regulatory status reflects a determination that either safety has not been demonstrated or that potential risks outweigh any technological benefits. Other authorities such as the Joint FAO/WHO Expert Committee on Food Additives (JECFA) maintain searchable databases of additives and contaminants, but thiourea does not appear as an approved food additive in the global JECFA compilations of permitted compounds. Instead, it remains excluded from lists of permitted compounds due to its prohibition or lack of safety data supporting use in food.

Taste And Functional Properties

Thiourea itself is a crystalline solid with chemical properties characteristic of small thiocarbonyl compounds. It is moderately soluble in water and polar organic solvents and can participate in various chemical interactions typical of sulfur-containing molecules. Sensory descriptions from chemical data indicate a bitter taste, but these notes come from handling data rather than culinary applications, since the compound is not used in foods. In functional contexts outside food—such as organic synthesis or industrial chemical processing—thiourea may complex with metals or act as a reducing agent, but these behaviors are unrelated to food processing since regulators prohibit its use in food products.

Acceptable Daily Intake Explained

Acceptable daily intake (ADI) is a concept used by food safety regulators to express the estimated amount of a substance that can be ingested daily over a lifetime without appreciable health risk. In the case of thiourea, because it is explicitly prohibited from use in food, regulatory bodies have not established a numerical ADI for dietary exposure. This absence reflects a lack of safety data demonstrating a threshold of safe intake for human consumption and the regulatory decision to exclude the compound from food use entirely. Consequently, the ADI concept does not apply in the same way it does for authorized food additives.

Comparison With Similar Additives

Comparing thiourea to other antimicrobial agents illustrates why it is excluded: authorized antimicrobial food additives such as sodium benzoate or sorbic acid have undergone rigorous safety reviews and have defined acceptable use levels in specific food categories, supported by toxicology data and international evaluations. By contrast, thiourea has toxicological concerns and insufficient safety evidence for dietary exposure. This comparison underscores that not all chemicals with antimicrobial properties are safe or suitable for food applications; regulatory frameworks distinguish permitted additives from those like thiourea that are outright prohibited due to safety uncertainties or documented hazards.

Common Food Applications Narrative

Because thiourea is listed specifically as a prohibited substance in the United States Code of Federal Regulations for food additives, it does not have accepted applications in food products. This means that in practice you will not find thiourea intentionally added to commercially available packaged foods, beverages, condiments, dairy products, or other edible items. Food manufacturers and ingredient suppliers must comply with regulatory lists of permitted additives, and substances like thiourea appear on exclusion lists precisely to prevent their use. As such, consumers and industry professionals alike should understand that this compound’s presence in food would indicate noncompliance and potential adulteration.

Safety & Regulations

FDA

  • Notes: Thiourea is listed as prohibited from direct addition to food under this section.
  • Regulation: 21 CFR 189.190

EFSA

  • Notes: No EFSA approval or E number is documented for thiourea.

JECFA

  • Notes: No JECFA evaluation establishing an ADI is available for this prohibited substance.

Sources

Comments

No comments yet. Be the first to share!