Shower steamers and shower melts are designed to dissolve completely in the shower. Citric acid acts as a natural preservative that can keep the steamers fresh for longer.  Citric acid also activates the fizzing reaction when warm water touches the shower steamer. Although having the shower steamer fizz on the floor of the shower when it gets wet isn't necessary, it is a fun reaction! However, if you do not have citric acid to include in your recipe, your shower steamers will still turn out and work well.