How do I choose a serum for oily skin?

For oily, blemish-prone skin, a Salicylic Acid 2% or Niacinamide 10% + Zinc 1% serum is a sensible starting point: both are formulated to help control excess oil and refine the look of pores. Apply to clean skin before moisturiser, and start every other day while your skin adjusts.

Which LOYI serum is best for brightening?

For a brighter-looking, more even tone, LOYI offers a Vitamin C serum for morning use and a Glutathione serum that can be used day or night. Give any brightening serum several weeks of consistent use, and always follow daytime use with sunblock.

Can I use more than one serum?

Yes, but introduce them one at a time so you can tell how your skin responds. A simple approach is one active in the morning (for example Vitamin C) and a different one at night (for example Retinol). Avoid layering several strong actives on the same night when you are still building tolerance.