According to WebMD, most eyeliners are made of film formers, thickeners and pigments. Eyeliners are used to emphasize the eyelids and change the perceived shape of the eyes.
Film formers deposit a thin layer on the skin. Thickeners usually come in the form of waxes, natural gums and clays, and help to stabilize the formula so it sticks to the eyelids. Pigments include iron oxides to create blacks and browns, ultramarine for blue, chromium oxide for green, and titanium dioxide for white. Eyeliners come in either pencil, liquid or cream form. Liquid liners are the easiest to handle and can be used to create a clean line. Creams and gels usually require a brush, and they can be smudged to create a smoky look or applied in a heavier line along the lid. Pencils tend to be waxier than other liners, making them more likely to smear.
According to Cosmetics Info, the ingredients in eyeliners are assessed for their potential to cause skin irritation or allergic reactions. The FDA issued an alert for eye makeup products such as kohl, kajal, al-kahl and surma. These traditional eye makeup products often contain lead and are not permitted in any cosmetic or personal care product in the United States for safety reasons.