The long, hot shower in summer looks like a reward - especially when it is hell outside and water is the only escape. But dermatologists have an unpopular message: what you experience as caring for your body, your skin experiences as an attack.

Dr Javier Pedras, a dermatologist, puts the rule plainly: "The ideal shower lasts between five and ten minutes." Anything over ten minutes starts stripping away the natural lipids that build the skin's protective barrier - the same barrier that keeps it hydrated and healthy. The result is dry, tight, more vulnerable skin. The opposite of what a shower is supposed to do.

Hot water makes all of it worse. It speeds up moisture loss and disrupts the barrier more strongly than lukewarm water. So the double mistake - long and hot - is exactly what most people reach for when the heat hits.

Those who feel it fastest are people with sensitive skin, with atopic conditions, rosacea or dermatitis. In them the damage shows earlier, but that does not mean the rest are spared - the effect just arrives more quietly.

The sentence worth remembering is blunt: "The skin is not cleaner because it spent more time under water; in fact, an excessively long shower can damage the very thing that keeps it healthy and protected." So washing is not a duration contest.

The recommendation is unromantic but simple: five to ten minutes, lukewarm water, a mild product in a small amount, and attention to the skin afterwards - if it feels tight or dry, the shower was too long. Summer calls for cooling off, but skin calls for measure. And measure, unfortunately, does not come with the pleasure of standing under the stream.