Butylated Hydroxytoluene vs Propylene Glycol: which is worse?

What is Butylated Hydroxytoluene?

Butylated hydroxytoluene (BHT) is a synthetic lipophilic phenolic antioxidant preservative derived from petroleum. It is a white crystalline solid with chemical formula C15H24O. Like BHA, it prevents fat oxidation and is widely used in food, cosmetics, pharmaceuticals, jet fuel, and rubber.

What is Propylene Glycol?

Propylene glycol is a synthetic organic compound used as a humectant, solvent, and emulsifier in food, pharmaceuticals, cosmetics, and industrial applications. It is produced from propylene oxide (derived from petroleum). Its chemical formula is C3H8O2.

Documented risks

Butylated Hydroxytoluene: BHT's carcinogenicity profile is complex and bidirectional. Some NTP bioassays found liver tumors in female mice at high doses, while other studies suggested BHT might inhibit tumor initiation in certain contexts. A 1986 NTP bioassay found liver tumors in female mice but anti-carcinogenic effects in the rat forestomach — making BHT's net carcinogenicity uncertain. IARC has not formally classified BHT in a specific Group due to this conflicting evidence. The NTP notes that BHT's carcinogenicity data are complex. The 'Report on Carcinogens' does not currently list BHT, unlike BHA, but the NTP has noted inconclusive evidence. Potential endocrine disruption: a 2017 study in Environmental Science & Technology found BHT disrupted thyroid hormone levels in female rats. Multiple animal studies have demonstrated weak estrogenic effects. The American Academy of Pediatrics' 2018 policy statement on food additives mentioned BHT as a synthetic preservative warranting reduced childhood exposure. Kellogg's Frosted Flakes in the US contains BHT to preserve freshness; the European version uses mixed tocopherols (vitamin E) instead — a commercially meaningful difference demonstrating feasibility of substitution. Japan banned BHT for food use based on its precautionary approach. The EU restricts it with ADI-based maximum permitted levels.

Propylene Glycol: Propylene glycol is generally considered safe by the FDA and is metabolized by the liver to lactic acid and pyruvate (normal metabolites). However, at high doses — particularly from intravenous pharmaceutical formulations — propylene glycol can accumulate and cause lactic acidosis, kidney toxicity, and CNS effects. These effects are seen in critically ill patients receiving high-dose PG-containing intravenous medications, not from food consumption. In children and people with impaired liver or kidney function, PG accumulation may occur at lower doses than in healthy adults. Animal studies have found reproductive and developmental effects at high doses. EFSA's 2018 re-evaluation found no concerns at typical food use levels but noted the EU limits PG use as a direct food additive, using it only as a carrier solvent for permitted additives.