What is Thiourea?
Thiourea is a simple organic compound with the chemical formula (NH2)2CS. It consists of a central carbon atom double-bonded to sulfur, with two amino groups attached. While the compound itself has legitimate industrial applications in photography, metal processing, and textile manufacturing, its use as a food additive has been prohibited in most countries.
Common Uses
Historically, thiourea was explored as an antimicrobial preservative in food products due to its ability to inhibit bacterial and fungal growth. The antimicrobial properties made it theoretically useful for extending shelf life in various food applications. However, this use was never widely implemented in commercial food production, and regulatory agencies acted to prohibit its food use before it achieved significant market penetration. Today, thiourea use in foods is not permitted in the United States, European Union, and most other jurisdictions.
Safety Assessment
Thiourea has been identified as a compound of toxicological concern, primarily due to its potential effects on the thyroid gland. Animal studies have demonstrated that thiourea can interfere with thyroid function and iodine metabolism. Additionally, thiourea has been shown to have goitrogenic properties—meaning it can promote goiter formation by interfering with thyroid hormone synthesis. Some research has also raised concerns about potential reproductive and developmental effects at high exposures.
The FDA has not granted thiourea GRAS (Generally Recognized As Safe) status. Notably, the FDA database shows zero reported adverse events and zero recalls associated with thiourea in foods, which likely reflects its prohibition rather than confirmed safety. Because the additive was prohibited before widespread use, there is limited real-world adverse event data from actual food consumption.
The toxicological profile, combined with the availability of safer alternative antimicrobial agents, led regulatory agencies to restrict or prohibit thiourea in food applications.
Regulatory Status
Thiourea is prohibited for use in food in the United States under FDA regulations. It is also not authorized as a food additive in the European Union. Most other countries follow similar restrictions. The compound is classified as a restricted chemical in food safety contexts due to its toxicological properties.
While thiourea remains commercially available for legitimate industrial, pharmaceutical, and laboratory uses, food manufacturers are prohibited from using it as a preservative or antimicrobial agent. Any food product containing thiourea would violate food safety regulations in major markets.
Key Studies
Toxicological research on thiourea has primarily focused on thyroid effects and endocrine disruption. Studies have documented thiourea's goitrogenic effects and its impact on thyroid hormone synthesis. The compound has been studied for potential reproductive and developmental toxicity in animal models. These scientific findings, rather than acute toxicity incidents, formed the basis for regulatory prohibition.
The decision to prohibit thiourea reflects the principle that food additives should be both effective and safe, with an adequate margin of safety. Given that safer alternative antimicrobial preservation methods exist—including approved food preservatives and modern food safety technologies—there is no practical need to use a compound with identified toxicological concerns.