Acid peels such as Glycolic Acid and Lactic Acid are Alpha Hydroxy Acids (AHA's) and are a less aggressive way to exfoliate the skin compared to a manual scrub which traditionally uses little particles to scrub at the skin. They are ideal for at home use. These acid peels work by helping to dissolve the glue like structure that holds dead skin on to the surface, allowing this dead skin to simply be rinsed away.
Salicylic Acid peel, which is a Beta Hydroxy Acid (BHA) is oil soluble, meaning it can penetrate through the skin's natural oil, travelling within the pores to help break down any oil and dead skin that is clogging up you pores. Salicylic Acid peel also has anti-inflammatory properties, meaning it can help reduce inflamed spots that can take a while to fade.