The skin is the largest organ in the body, which means we have to think carefully about what we apply to it. Any particles small enough to be absorbed through the top layer of our skin will ultimately end up in the bloodstream. This means that toxic ingredients applied to your skin have the potential to enter your body. A good rule of thumb is to never put anything on your skin that you wouldn’t consider ingesting (with obvious exceptions like sunblock or zinc, which are specifically designed with large enough particles to prevent absorption through the epidermis).

Substances routinely pass through the skin’s outer surface, enter deeper layers, and finally reach the bloodstream. This diffusion occurs when there is a high concentration of a substance on the skin’s surface and a lower concentration inside the body, allowing the particles to move inward. Once absorbed, these substances circulate throughout the body, reaching vital organs, muscles, and even the brain.

Watching what you put on your skin is just as important as watching what you eat, both allow new substances into the body, where they can either nourish or harm. Dermal absorption is one of the four primary routes of exposure, alongside inhalation, ingestion, and injection. For example, ink on your skin introduces toxic chemicals that your body must work to eliminate.