What first started as a tip from an influencer about using kojic acid soaps to lighten underarms has turned into a full-blown craze. But with all the hype around kojic acid products, you may be wondering what it is in the first place. Below, you can also find product recommendations and some helpful alternatives in case kojic acid isn't the right fit for you. Check out some of our favorie kojic products below:What skin types can use kojic acid? Side effects of kojic acidDr. Ahram suggests using products with one percent of kojic acid or less.