How do I know if a serum is actually working?

A working serum shows gradual, measurable improvement in the specific concern it targets over six to twelve weeks. For a vitamin C serum, you should notice a brighter, more even complexion. For retinol, smoother texture and softer fine lines. For niacinamide, reduced pore visibility and less oiliness. Take consistent photos in the same lighting every four weeks to track progress objectively — changes are often too gradual to notice day-to-day.