One of the most widespread stories in cosmetics is that "the skin gets used to the cream" and so it stops working. Dermatologist Lidia Maroñas, founder of Oneskinmed, is blunt: it's an absolute myth.

The misconception comes from two real phenomena, she says. One is tachyphylaxis - when certain drugs really do lose their effect over time. The other is simpler: the original problem has been solved, so it looks as if the product stopped working, when in fact it's just continuing to maintain what it already fixed. When one concern disappears, the eye notices a new one it wasn't looking at before.

Why do new products seem more effective? Hydration temporarily smooths the surface layer and softens fine lines - a visual effect that doesn't last long. And ingredients like retinol or acids initially trigger a reaction that speeds up skin renewal, even though the real anti-ageing effect builds over months. Glycolic acid gives a quick visible result; retinoids and antioxidants demand patience, sometimes even irritation, before they stimulate collagen over 6 to 12 months.

The point is simple and the opposite of what the industry wants you to believe: you don't have to keep changing products and spending on the latest miracle in a bottle. A routine is worth reviewing every three or four months, with the change of seasons - and only if you have dryness, acne, new spots or are pregnant. Everything else is marketing, dressed up as science.