Essential oils disrupt steroidogenesis in a feto-placental co-culture model.

•Basil and fennel seed essential oils disrupt fetal-placental steroidogenesis.•Essential oils can increase hormone levels and genes involved in hormone biosynthesis.•Basil and fennel seed essential oils induced CYP19 expression and catalytic activity.•Lower concentrations of essential oils had greater steroidogenic effects.•Sweet orange, sage, and black pepper essential oil had no steroidogenic effects.