An active ingredient is a substance in a product that has an effect on the body. It can affect one part of the body (such as the skin) or the entire body.
A product can have more than one active ingredient. The active ingredient of a product is listed on its box or packaging. Also, the amount of active ingredient is usually listed.
A product can also contain inactive ingredients that do not have an effect on the body. Inactive ingredients can help with the delivery of the active ingredient or do other things such as prevent the product from spoiling. These are often listed after the active ingredient in the ingredient list.