For years we've been told that blue light from screens "ages" the skin. The cosmetics industry built an entire product category on it. Now experts say the problem usually isn't the laptop but the window next to it.

"I wouldn't equate eight hours in front of a computer with eight hours in the sun. From the skin's point of view, working next to a window without sun protection is far more worrying than the screen itself," explains Mireia Fernandez, dermo-cosmetic director at the brand Perricone MD. The high-energy light that screens emit can cause oxidative stress, but the damage is nowhere near that of too much sunbathing.

Glass is not a shield

One of the most common mistakes when working from home or in an office is believing that sun protection isn't needed if we don't go outside. Some ultraviolet rays - above all UVA - pass through glass, and the consequences are the same: dark spots, dehydration, expression lines and wrinkles appearing sooner, and dull skin. So the rule is simple: whatever the weather and however much time we spend outdoors, a cream with SPF in the morning is insurance for both the health and the look of your skin.

Frowning at the screen shows up in the evening

Another factor is the face we pull at the screen, day after day. "Squinting to read, frowning or staring for long periods makes some expression lines more visible by the end of the day. In the morning they may go unnoticed, and in the evening look far more pronounced, especially if the skin is dehydrated," says Irene Serrano, dermo-cosmetic director at Dermalogica. She also points to the air: when skin spends hours in a dry environment, with air conditioning in summer or heavy heating in winter, it becomes tight and rough, and fine lines show more. "It doesn't mean there are more wrinkles: skin with less water simply shows them more."

Against dehydration, for radiance and against oxidative stress, besides sun protection, experts recommend antioxidants - vitamins C and E, glutathione and ferulic acid. Fernandez is sceptical about spritzing your face with a mist every twenty minutes: "It makes more sense for your morning routine to limit water loss. Hyaluronic acid, glycerin or beta-glucans help hold on to water, while ceramides, squalane and other lipids strengthen the barrier."

Estefania Nieto, dermo-cosmetic director at Medik8, adds habits that cost nothing: short breaks, a few deep breaths, consciously relaxing the jaw and forehead, and looking further away from the screen. "It's not an anti-ageing treatment, but it helps you not hold that tense expression for hours."

It's worth keeping in mind who's talking: all three experts work for cosmetics brands that sell products for precisely these problems. That doesn't mean they're wrong - the effect of UV rays through glass is well known. But the cheapest advice in the whole story doesn't come in a bottle: if your desk is next to a window, a curtain and SPF in the morning do more than any "blue light" serum.