Eight Weeks, One Change at a Time

Skin turns over on roughly a four-week cycle, and inflammation from a new active takes two to three weeks to settle. Any verdict delivered inside a fortnight is describing irritation, not outcome. Eight weeks is the shortest honest window, and only if exactly one variable moved.

The protocol

• Weeks 1–2 — baseline. Cleanser, one bland moisturiser, sunscreen. Nothing else. Photograph the same cheek at the same time of day, by a north window, no flash.
• Weeks 3–8 — introduce one product. Same cleanser, same moisturiser, same sunscreen. Two applications a week for the first fortnight if it is an active.
• Log three things — visible flake, stinging on application, and whether makeup sat differently. Those three catch almost every real reaction.

Concentration is not potency

A 10% vitamin C serum at pH 3.8 in an anhydrous base and a 10% serum in water at pH 5.5 are different products with the same front label. Ascorbic acid needs a low pH to cross the barrier and oxidises in water; the second one is a moisturiser with a marketing budget. Retinal at 0.05% typically outperforms retinol at 0.3% because it is one conversion step closer to retinoic acid.

Read the INCI list in order. Anything below the fragrance line is present in fractions of a percent, whatever the front of the box says about it.

What we saw over a year

The dullest intervention won. Daily sunscreen did more for even tone over six months than every serum we tested, and it did it without a two-week irritation phase.