Propylene Glycol vs Red Dye 40: which is worse?

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.

What is Red Dye 40?

Red Dye 40 (Allura Red AC) is a synthetic petroleum-derived azo dye that produces a bright red-orange color. It belongs to the monoazo chemical class and is highly water-soluble, with the formula C18H14N2Na2O8S2. It replaced amaranth (Red Dye 2), which was banned in the US in 1976 following cancer concerns.

Documented risks

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.

Red Dye 40: Red Dye 40 has been linked to several health concerns, particularly in children. The most documented association is with hyperactivity and ADHD-related behavior. A landmark 2007 study in The Lancet (McCann et al.) found that a mixture of six artificial dyes including Red 40, combined with sodium benzoate, significantly increased hyperactivity scores in children ages 3 and 8–9. This prompted EFSA to require the 'may have adverse effect on activity and attention in children' warning label across the EU and UK. A 2012 meta-analysis in Neurotherapeutics (Arnold et al.) confirmed a small but statistically significant deleterious effect of artificial food colors on children's behavior, even in those without diagnosed ADHD. The authors described the effect as a public health issue rather than merely an ADHD issue. Regarding carcinogenicity: commercial batches of Red 40 contain trace amounts of benzidine, an IARC Group 1 human carcinogen. A 1994 study in Food and Chemical Toxicology documented benzidine contamination. The FDA maintains that exposure is below harmful thresholds, but the Center for Science in the Public Interest (CSPI) has cited this contamination in multiple ban petitions. Allergic reactions are documented: Red 40 can trigger histamine release leading to hives, rhinitis, and in rare cases anaphylaxis. Cross-reactivity with aspirin is established in aspirin-sensitive individuals. Gut health: A 2021 study in Nature Communications (Kwon et al.) found Red 40 may worsen inflammatory bowel disease and induce colitis-like symptoms in genetically susceptible mice by triggering immune responses in gut-associated lymphoid tissue. In April 2025, HHS Secretary RFK Jr. announced the FDA would phase out Red 40 and 7 other petroleum-based dyes from the US food supply.