Prof. John Dart from the UCL Institute of Ophthalmology had the following to say: “Mascara, like many cosmetics, contains a lot of components, many of which are potentially toxic: Carbon black or iron oxide pigment to darken lashes; a polymer to form a film that coats lashes; a preservative; and thickening waxes or oils such as lanolin, mineral oil, paraffin, petrolatum, castor oil, carnauba wax, and candelilla wax.”
Dart says it isn’t a big deal if you sleep with your makeup on for one night. You should, however, make a habit out of washing your makeup off before bedtime.
He also says that you should not share your mascara with others.
If you leave your eye makeup on at night or if you know somebody that does so regularly, this is a good warning.
Having some makeup removal wipes handy will help you to get the job done, even if you come home tired.