Tert-Butylhydroquinone (TBHQ, tertiary butylhydroquinone) is a synthetic aromatic organic compound which is a type of phenol. It is a derivative of hydroquinone, substituted with a tert-butyl group. TBHQ is commonly used in foods such as cooking oils, frozen meats (especially fish) and processed foods such as chips and crackers. It has been used in foods for many decades and serves no function besides increasing a product’s shelf life. TBHQ is added to foods to prevent or delay oxidation. Oxidation causes food to lose flavour quality, colour and can even cause foods to become toxic. In addition, oxidation causes vitamins to break down, causing food to lose some of its nutritional value. TBHQ can increase shelf life and reduce food waste from food spoilage.

In 2021, a study by the US Environmental Working Group (EWG), analysing data from the Toxicity Forecaster (ToxCast), showed that the preservative TBHQ is harmful to the immune system, based on both animal studies and in vitro toxicological studies. This finding is particularly worrying in the time of the coronavirus pandemic. The EWG recommends that immunotoxicity testing of chemicals in food and food contact materials be prioritized to protect public health from their potential adverse effects on the immune system.

Earlier studies have found that TBHQ might influence how well flu vaccines work and may be linked to a rise in food allergies. In 2019, Michigan State University scientists have linked TBHQ to an altered immune response that possibly hinders flu vaccines. The researchers looked at several response factors including whether the T cells showed up, were able to do the right job and ultimately, recognize and remember the invading virus. Overall, they saw a reduced number of CD8 T cells in the lung and a reduction in the number of CD4 and CD8 T cells that could identify the flu virus in the mice that were exposed to TBHQ. The mice also had widespread inflammation and mucus production in their lungs. TBHQ also slowed down the initial activation of T cells, reducing their ability to fight off an infection sooner. A second phase of the study showed the additive hindered the immune system's ability to remember how to respond to the flu virus, particularly when another strain was introduced at another time. This resulted in a longer recovery and additional weight loss in the mice.

While there was concern in the 1980s and 1990s that high-dose TBHQ experiments caused cancer in animal models, in 2004 the European Food Safety Authority (EFSA)'s scientific panel concluded that TBHQ is not carcinogenic. This finding has been endorsed not only by EFSA, but also by other leading regulatory and health bodies around the world, such as the US Food and Drug Administration (FDA) and the Joint FAO/WHO Expert Committee on Food Additives (JECFA). To further explore the issue, researchers have conducted scientific research and testing to determine the safety of preservatives. Comprehensive studies can help to determine whether additives can be used safely in food, are safe in the human body and have health effects. After the FDA approved the preservative, scientists set guidelines for the amount that can be safely incorporated into foods and the maximum amount that people can consume. The FDA determined that the TBHQ content of a food should not exceed 0.02% of the total fat and oil content. The acceptable daily intake (ADI) for consumers is 0.7 mg/kg bw. This limit has been agreed internationally and the EFSA confirmed the same ADI in 2004.

In 2016, EFSA's Panel on Food Additives (ANS) confirmed that while exposure in adults does not exceed the ADI, exposure in infants may exceed the previously accepted daily intake. Subsequently, the ANS carried out a refined assessment of TBHQ exposure based on a comprehensive analysis of data from the European Food Consumption Database and newly submitted data on actual use. Based on the results, ANS concluded that using the maximum permitted levels, the exposure for infants and children exceeds the ADI of 0.7 mg/kg bw/day, but for the refined exposure scenarios the ADI was not exceeded in any age group.

Given the above, it would be useful to further investigate the effects of TBHQ on the immune system.