Bentonite clay is very alkaline and has a PH level of approx 8.6 to 9. Your skin has a natural PH of approx 5.5. When you apply a skincare product to your skin that is too alkaline, this can cause redness and a poor skin reaction. Mixing your bentonite clay with an acidic ingredient like apple cider vinegar can balance the PH of your bentonite and ACV face mask.