Every season the cosmetics industry announces the molecule that will change everything. This year it is NAD+, a coenzyme that genuinely exists and genuinely does important work in the body - it produces cellular energy and takes part in repairing damaged DNA. The problem starts when that gets translated into a bottle.

Dermatologist Natalia Jimenez said the thing the adverts do not put in the headline: "This molecule struggles to cross the skin barrier because it is large and unstable." In other words, if the label says NAD+, that does not mean NAD+ is getting into your skin. It is not.

Which is why the formulas do not work directly. They use precursors - smaller molecules the skin can absorb and then convert into NAD+ itself. The most common is niacinamide, vitamin B3, an ingredient that has been in cosmetics for decades, long before NAD+ became a name on a box. That does not mean the products do not work. It means what works is not the new part.

Jimenez also points to a shift in what counts as good skin in the first place. The measure used to be wrinkles. Today the talk is of balance, of glow, of skin health - categories that are harder to measure and easier to sell. That this coincides with the industry's need to create new criteria is a coincidence worth noting.

Practically, there are three ways to use it and all three are reasonable. During the day, combined with antioxidants like vitamin C, if the problem is pigmentation. At night, in a serum, when cells regenerate. And through a day cream with sun protection factor, which remains the cheapest and most effective thing you can do for your skin, no matter how many molecules get piled on top of it.

The prices tell the other half of the story. A serum with NAD+ costs around 64 euros. A cream with a similar purpose from a large cosmetics house - 195 euros. That is a threefold spread for products whose active mechanism is identical: niacinamide, which the skin converts into something else.

The recommendation is from age 35 upwards, which is early enough to catch a lot of people and late enough to sound expert. If you want one rule out of the whole text, it is this: check what the ingredients list says, not what the front of the box says. The front is marketing. The back is the recipe.