Lactic acid is produced via the fermentation of a cultured bacteria via biotechnology. It is a liquid solution in water.
Lactic Acid is a strong Alpha-Hydroxy Acid and hence will have excellent exfoliant properties, although weaker than Glycolic Acid. AHA products should be a stand alone treatment product and not included in another product. While AHA can be included in other products there are certain incompatibilities that may arise plus AHAs (because of the pH required for best effectiveness) may not allow other products (such as cleansing masks) to work properly, and vice versa. AHA products should have a pH of 3.5 to 4.5 for best effectiveness (Note at pH 7 AHAs are totally ineffective).
AHAs are generally a face treatment and not to be confused with a cleanser. You should clean the face first and then apply the AHA treatment.