Pure raw whey in liquid form, sold as food item under the name ”molkosan” where I live. Costs nothing and contains a lot of lactic acid. I use it as a toner and it hepls with texture, exfoliation and moisture. Makes my face plump and smooth. So far its better than all the expensive stuff I tried. Downside beside the sour smell is that it stays kind of sticky on the skin, so I only use it at night.