سيروم وأمبولات

Mostly concentration and bottle size. Ampoules tend to be stronger and sold for a defined course; serums are the everyday step. Neither name guarantees anything about strength on its own — read the actives.

Two is comfortable for most people, one in the morning and one at night. Three is possible if they don't conflict. Beyond that you're mostly diluting your own routine.

Yes. Serums deliver actives; they don't seal. Skipping the moisturiser is why some people find serums drying.

Vitamin C and niacinamide in the morning. Retinoids at night, always. Hydrating serums either or both.

Hydration, days. Oil control and texture, four weeks. Pigmentation and fine lines, eight to twelve. Stopping at three weeks is the most common reason people conclude a good serum did nothing.