Ajaya Kashyap, MD says:Thanks for your query. Yes glycolic acid and tns serum can be used together at night. Glycolic acid acts as a skin lightening agent and tns serum mainly consists of Human Fibroblast Conditioned Media, Water (Aqua), Cetyl Ethylhexanoate, Olea Europaea (Olive) Fruit Unsaponifiables, Alpha-arbutin,...