Sulfur is a safe FDA-approved ingredient. It works to counter acne by reducing the bacteria that cause acne, and it also removes dead skin cells and excess oil. Sulfur is quite safe when applied to the skin appropriately. Products containing sulfur in concentrations of up to 10% have been used safely for up to 8 weeks. We recommend that you do not skip using a moisturiser the next day after using the Overnight Acne Spot Corrector, since Sulfur helps dry out the surface of your skin to help absorb excess oil (sebum). It is important to add back the moisture to your skin as part of your overall skin care to avoid dryness and breaking skin.