Citric acid otherwise known as sour salt due to its resemblance to table salt are used to resurface the complexion to eliminate fine lines, wrinkles, scars and areas of skin discoloration. By removing the dead cells that often clog the pores, citric acid can also be beneficial for people suffering from acne or enlarged pores.
Citric Acid is an essential ingredient in making bath fizzies and bath bombs. The reaction between the citric acid and baking soda (sodium bicarbonate) result in a delightful effervescence when added to water. Citric Acid can also be used to reduce the pH of your handmade soap. In cold process soap it is dissolved and added at trace. You can also use citric acid to reduce the pH in liquid soap by creating a 20% dilution in water and mixing a small amount into your liquid soap. Be careful to add very small amounts slowly as adding too much can cause the soap to thin out and separate.
Source: skinstore.com, brambleberry.com