Reproductive harm in male animals
A 2002 study fed propylparaben to young male rats for four weeks and found that daily sperm production fell significantly at every dose tested, including the lowest dose, which matched the upper limit of the old acceptable daily intake. Testosterone also dropped in a dose-dependent manner. Because no dose was found that caused no harm, it was impossible to set a safe intake level. This finding was the primary reason EFSA withdrew authorisation for the additive.
Daily sperm production and sperm reserves fell in a dose-dependent manner in young male rats given propylparaben; all treatment groups showed significant reductions in daily sperm production, leaving no identifiable no-effect level.
2002AnimalOishi S, Food and Chemical Toxicology, volume 40, pages 1807-1813
EFSA concluded it could not set an acceptable daily intake for propylparaben because no clear no-observed-adverse-effect-level existed for the reproductive endpoint in juvenile rats.
2004Regulatory reviewEFSA Scientific Panel on food additives (AFC), Opinion on para-hydroxybenzoates (E 214-219), EFSA Journal 83
The Joint FAO/WHO Expert Committee on Food Additives (JECFA) withdrew propylparaben from the paraben group acceptable daily intake following review of the same reproductive toxicity data.
2006Regulatory reviewJECFA 67th meeting, Food additives summary and conclusions, FAO/WHO
Weak oestrogen-like activity
Parabens bind to oestrogen receptors and produce oestrogen-like effects in laboratory and some animal tests, though the potency is far lower than natural oestrogens. The longer the alkyl chain, the stronger the oestrogen-like activity, placing propylparaben between methyl- and butylparaben in potency. A 2021 European scientific committee reviewed this evidence and concluded the available data showed indications of potential endocrine effects, but was insufficient to formally confirm propylparaben as an endocrine disruptor in humans.
Propylparaben shows oestrogenic activity in vitro and in uterotrophic assays; oestrogenicity increases with alkyl chain length across the paraben series.
2008Lab + animalDarbre PD and Harvey PW, Journal of Applied Toxicology, volume 28(5), pages 561-578
A 2021 EU Scientific Committee on Consumer Safety opinion concluded there was insufficient data to conclusively confirm propylparaben as an endocrine-disrupting substance, while acknowledging the potential for endocrine effects remains.
2021Regulatory reviewSCCS Opinion on Propylparaben, SCCS/1623/20, European Commission
Detection in human breast tissue
Parabens including propylparaben have been detected intact in human breast tumour tissue. The 2004 study that first reported this used 20 samples with no comparison group of healthy tissue, so it could not show whether paraben levels differ between cancerous and non-cancerous breast, and could not distinguish food exposure from cosmetic or pharmaceutical sources. Subsequent larger studies confirmed parabens accumulate in breast tissue but causality has not been established.
Parabens including propylparaben were found intact in 20 human breast tumour samples; mean total paraben concentration was 20.6 nanograms per gram of tissue. The study had no healthy tissue control group and could not determine the source of exposure.
2004ObservationalDarbre PD et al., Journal of Applied Toxicology
Prenatal exposure and child neurodevelopment
Observational cohort studies have measured propylparaben in pregnant women's urine and followed their children's cognitive and behavioural development. One prospective cohort study found associations between higher prenatal propylparaben exposure in the second and third trimesters and lower cognitive development scores at age 3 in female children. The cohort was enriched for autism risk, the sample was small (130 children), and results are inconsistent across cohorts. Confounding from other chemical exposures cannot be ruled out. No causal link has been established.
In a prospective cohort enriched for autism risk, higher prenatal propylparaben exposure in the second and third trimesters was associated with lower standardised developmental scores at age 3 in female children (approximately 2.57 units lower at the 75th vs 25th percentile of exposure); the sample included 130 children.
2024ObservationalMARBLES Study cohort, Science of the Total Environment, PMC10960968