As a general rule, apply water-based serums first, followed by anhydrous (oil-free but non-water) or oil-based formulas, and finally creams/suspensions. Limit your routine to 3 serums per regimen to prevent pilling.

It is recommended to use them at different times of the day (e.g., Vitamin C in the morning and Niacinamide in the evening) because pure Vitamin C (L-Ascorbic Acid) can be degraded when mixed directly with Niacinamide.

The Ordinary offers high concentrations of active ingredients. Patch testing helps identify potential sensitivities or allergic reactions before applying the product fully to your face.