If you have just come back from holiday, you know the moment: the suitcase open, the laundry pile growing, and all of it going into the machine together. The swimsuits go in with everything else, and at the start of the next summer somebody wonders why they have lost their colour and gone slack.

Chlorine, salt, sunscreen and the sun itself wear them down year after year. There is a way to avoid that, and it needs nothing you do not already have in the kitchen.

Advice picked up in Brazil, used for seventeen years

The trick is shared by Merce Bona, a content creator with over ten million followers across her channels. "This is the definitive recipe for making your bikinis and swimsuits last a lifetime," she claims in one of her most watched videos this summer.

The claim is not empty: she has pieces she has kept for seventeen years. The most frequent question her followers ask is exactly that - how it is possible for them to last so long without losing their colour or having the fabric stretch out. The answer, she says, came to her at twenty, on a trip to Brazil, from a shop assistant in a local store when she bought a bikini. She has applied it at the end of every summer since.

The method, step by step

Fill a bowl with cold water. Add a little apple cider or white vinegar. Add baking soda, about two tablespoons. Finally add a little salt and stir. Soak the pieces in that mixture for five to ten minutes. Rinse them with water and leave them to air dry - but in the shade, not in the sun.

The most important detail is when you do it. "You should only do this at the end of summer, when you are storing the swimwear until next year, not every time you use it," she points out. So it is not a routine, it is one move a year.

Why it works

This is not magic but chemistry, and the explanation is specific. "The vinegar will neutralise any chlorine left in the garment, and the baking soda will prevent bad odours from building up, and beyond that it disinfects and cleans. The salt will help fix the colours," Bona says.

Then the storage: in a drawer, organised with dividers - not in plastic or fabric bags.

Fabric softener is the quiet culprit

Here comes the part most people do every day without thinking. As with sportswear, fabric softener can work against you, affecting the elasticity of the fabric.

"Softeners can leave residues on clothing over time, especially if used excessively. Those residues can build up in the fabric fibres, reducing their capacity to absorb and breathe," note representatives of one textile company.

The claim is that the trick works with swimwear of different quality - both premium brands and cheaper ones. That is the part worth testing yourself, because the industry has an interest in swimwear lasting one summer. If it lasts seventeen, sales fall seventeenfold.