New jeans already losing color? Why adding salt won't help and what actually works

New dark jeans, a red sweater, a navy bath towel: before the first wash, many people still throw a handful of salt or a splash of vinegar into the washing machine to "set" the color.

It's a trick passed down through generations, and you'll still find it recommended on laundry websites. But Iowa State University's Extension and Outreach service has a less romantic explanation.

Salt really is used when coloring fabric, but that happens during manufacturing. Once the garment is finished, adding salt to the wash won't lock in the color. So why do so many people believe it works? And what should you do instead?

Why salt is used to dye clothes

The old advice isn't entirely made up. Salt genuinely plays an important role in textile production, particularly when dyeing cotton.

During manufacturing, salt helps move dye from the water onto the fabric fibers, making it easier for the material to absorb the color. It's part of a carefully controlled chemical process.

However, that doesn't mean adding table salt to your washing machine has the same effect.

With certain dyes used on cotton, the color becomes chemically bonded to the fibers during production. As explained in published textile research, salt helps the dye reach the cotton, while other chemicals and conditions allow those bonds to form.

Once the clothing has been dyed and manufactured, those bonds have already formed. A handful of salt won't strengthen them or permanently attach any remaining loose dye.

And vinegar? According to textile experts, acids can help set certain dyes during the original dyeing process. But pouring vinegar into the wash afterward doesn't provide that same protection.

Why grandma's trick sometimes seemed to work

There's a good reason people have believed in the salt trick for decades: their clothes sometimes stopped bleeding after they tried it.

But the salt probably wasn't responsible. New clothes, especially dark jeans and brightly colored fabrics, can contain excess dye that wasn't properly attached during manufacturing.

During the first few washes, some of this loose dye gets rinsed away. Afterward, the garment may release noticeably less color.

Experts explain that when salt or vinegar appears to work, it's often simply because those loose dye remnants have been washed out. The water and washing process did the job, while the household remedy received the credit.

That doesn't mean every garment will eventually stop bleeding. Some poorly dyed fabrics can continue transferring color, even after repeated washes.

What actually stops new clothes from bleeding?

Fortunately, protecting your laundry doesn't require any unusual ingredients. A few changes to your washing routine can make a real difference.

Wash new clothes separately. Particularly dark or brightly colored items should be washed alone or with similar shades for their first few washes. This helps remove excess dye without staining your other clothes.

Choose cold water. Hot water can encourage dye to escape from fabric. Use a cold cycle when the care label allows it.

Try the white cloth test. Before washing an unfamiliar garment, dampen a clean white cloth and rub it against a hidden seam. If color transfers, keep the garment away from lighter laundry.

Consider color-catching sheets. These specially treated sheets absorb some of the loose dye floating around in the wash water. Iowa State University says they can help reduce color transfer, although they're not completely reliable. They also won't prevent the original garment from losing dye.

The best way to protect your dark clothes

For particularly bright new garments, some laundry guides also suggest a cold-water soak before the first wash. However, soaking isn't a way to permanently fix dye, and it should only be done when the fabric's care instructions allow it.

The most reliable approach is still surprisingly ordinary: follow the care label, sort your laundry carefully, and keep new dark clothes away from whites until you're confident they won't bleed.

Grandma may have had plenty of useful household tricks, but when it comes to keeping your new jeans dark and your white shirts white, you can leave the salt in the kitchen.