Parabens are a class of preservatives commonly used in all kinds of skincare and makeup products to prevent the growth of bacteria and mold. Essentially, you want to avoid anything ending in -paraben, since they mimic estrogen and may play a role in triggering cancer and other serious health issues.
They are problematic because they mimic estrogen and can disrupt the hormone (or endocrine) systems. While studies have found parabens in almost all urine samples taken from a demographically diverse sample of U.S. adults, adolescents and women had higher levels of methylparaben and propylparaben than males of similar ages. Teens and women use more cosmetics than men, so this is likely the reason. Parabens have also been found in breast cancer tissue.