What is the best order to layer serums?

When using multiple serums, apply them in order from thinnest to thickest and from most active to most supportive. A common sequence is: antioxidant serum (vitamin C), treatment serum (retinol, AHA, or BHA), then hydrating serum (hyaluronic acid or niacinamide). Avoid layering two highly active serums simultaneously unless your skin has built tolerance. Waiting 30–60 seconds between serum layers allows each to absorb before the next is applied.