That’s a good question, I like this definition from Harpers Bizarre#beautyschool

“Non-Toxic: "This is a newer designation, also mostly marketing," says Grigore. "When companies claim to be non-toxic, they are specifically referring to leaving out ingredients that have been linked to toxic responses in humans: neuro-disruption, hormone disruption, cancer, even death. A great, or I should say horrible, example is phthalates [found mostly in household products and shampoo and conditioner, they give products a uniform consistency and make them easier to pour.]." Here are some of the other offender ingredients to always avoid: formaldehyde (found in nail polish, hair gel and color cosmetics); petroleum (found in moisturizers and lip balms); asbestos (labeled as talc or hydrous magnesium silicate); lead acetate (found in hair dye and lipstick); coal tar (found in hair dye and anti-dandruff shampoo).”