Serums

Two is plenty for most people, three at a push. Beyond that you cannot tell what is working, and the chance of irritation goes up.

A straightforward approach is an antioxidant serum in the morning and a treatment serum at night.

Thinnest to thickest, and water based before anything oil based. Give each one a moment to absorb rather than layering straight away.

If two serums both contain strong actives, it is usually easier to split them between morning and evening than to layer them.

If you are building a routine from nothing, a vitamin C in the morning and a hydrating serum whenever skin feels tight. SkinCeuticals HA Intensifier Multi-Glycan and Obagi Daily Hydro-Drops are both easy first steps.

Then add one treatment serum for your main concern, whether that is pigmentation, blemishes or loss of firmness.

Mostly concentration and texture. Essences are lighter and more watery, usually used for hydration straight after cleansing. Ampoules are more concentrated and often used in shorter courses.

Serums sit between the two and are the workhorse of most routines.

Yes, though not in the same application while you are getting used to them. Vitamin C in the morning and retinol at night is the simplest way to have both.

Once your skin is settled, plenty of people use them in the same evening without any trouble.

Hydration shows within days. Brightness and tone take four to eight weeks. Firmness and fine lines take twelve weeks or more.

Finish the bottle before you judge it, and change one thing at a time so you know what actually did the work.