Most mascaras are made of pigments that darken lashes, such as carbon black or iron oxide. Mascara contains polymer that coats the lashes, a preservative to keep it from spoiling and a wax or oil to keep it thick, such as lanolin, mineral oil, paraffin, petrolatum or candelilla wax.
Lash darkeners from the 1930s used to contain ingredients like turpentine, lead-containing kohl and a hair-dye ingredient called aniline. After it had been proven that many women were blinded by those ingredients, strict regulations were put in place in America that limited the ingredients for safety. However, thimerosal is a hazardous material that can still be found in some brands of mascara. It has been proven to cause conjunctivitis and eyelid dermatitis.
Waterproof mascara does not usually contain water or emulsions of water and oil, making them harsher for lashes and difficult to remove. This is due to the fact that emulsions tend to flake or smudge. According to the FDA, the use of waterproof mascara should be limited by consumers because of the effort required to remove the product. Overuse can cause lashes to either become brittle and break or fall out. Regrowth can take time, and some people reported growth had completely stopped.