‘Antibacterial’ sportswear can lose its silver in the wash, and a wear test found it no fresher

In one experiment, Benn and Westerhoff bought six pairs of name-brand anti-odour socks impregnated with nanosilver.¹ Nanosilver is silver used as nanoparticles, tiny particles that work better against bacteria, so smaller amounts can be used.² They soaked the socks in a jar of room-temperature distilled water, shook it for an hour and tested the water for silver.¹

Some socks released all their silver in the first few washings, others released it gradually, and some released none at all.¹ That is what the word “antibacterial” on a clothing label does not tell you: the silver is an added germ-killer, not part of the fabric, and in many products it does not stay put.

In another study, researchers put silver-treated fabrics through a washing machine.³ Bernd Nowack, one of the researchers, summed up what they found: “We found that the total released varied considerably from less than 1 to 45 percent of the total nanosilver in the fabric and that most came out during the first wash.”^3,4

Dissolved silver, known as ionic silver, is only toxic to humans at very high levels, but the toxicity of the nanoparticle kind, Westerhoff said, has yet to be determined.¹

YAN’s view: skip clothes sold as antibacterial or anti-odour, above all for babies, because a freshness promise the evidence does not back is no reason to wear a germ-killer whose effects on skin nobody has worked out.

What you need to know

• Clothing sold as antibacterial or anti-odour can be treated with silver, which US regulators handle as a pesticide product in textiles.^4,5
• Some of that silver comes off in the wash, most of it the first time, and the amount varied considerably between products.^3,4
• When eight men wore silver-treated fabric, it did not lower odour intensity compared with the same fabric untreated.⁶
• EU scientific advisers found no studies on whether silver nanoparticles help germ resistance spread.⁷
• For babies and anything worn next to the skin, choose plain cotton with no finish claim.

What is the silver doing in my socks?

Silver is widely used for its antibacterial activity in medical and consumer products, because it works against a broad range of bacteria with lower toxicity than many other germ-killers.² It is thought to work by blocking the respiratory enzyme pathways bacteria use to breathe and by damaging their DNA and cell wall.⁴ In clothing the target is smell: one silver product proposed in the US was built into textiles to suppress bacteria, fungus, mold and mildew that cause odors, stains and discoloration.⁵

More and more products use silver as nanoparticles because, at that tiny size, it kills bacteria better, so lower amounts can be used.² Products containing nanosilver are difficult to track, because they are sold under numerous brand names.² That makes it hard for a shopper to know which clothes carry it.

In the US, silver for textiles goes through registration as a pesticide product, and a court has already thrown out one approval for a nanosilver ingredient.⁵ Whatever the label calls it, then, a regulator treats this silver as a germ-killing chemical added to the cloth, not a quality of the cloth itself.

Where the silver goes

Earlier tests had laundered socks only in pure distilled water.⁸ The majority of the silver left as relatively coarse particles rather than the very finest ones, which the researchers read as a sign of mechanical stress: the rubbing and tumbling of the wash.³ So most of the silver that comes out is scrubbed off the fibres by the wash itself.

A conventional silver textile, made without nanoparticles, shed silver in much the same particle sizes as many of the nano-treated fabrics.³ So choosing “non-nano” silver does not make the shedding question go away.

Different sock types leached silver at different rates, which suggests the manufacturing process may control how much gets out.⁹ Nowack saw a hopeful side to this: “it is possible to engineer nanosilver textiles so that only little silver is released during washing”.⁴ So two socks sold with the same silver claim may behave very differently in the wash.

The Empa study also found that bleaching agents such as hydrogen peroxide can greatly speed up how fast the silver dissolves.³ Researchers reporting at a national meeting of the American Chemical Society found that detergents containing bleach and bleach alternatives made the silver nanoparticles break down.¹⁰ Milder detergents had no such effect, but still washed the particles out of the fabric over time, possibly letting toxic ions into wastewater.¹⁰

Benn explained why that matters for rivers and the life in them: “If you start releasing ionic silver, it is detrimental to all aquatic biota. Once the silver ions get into the gills of fish, it's a pretty efficient killer.”¹

Does it actually keep clothes fresher?

In one study, eight male participants wore fabric with a germ-killing treatment against their armpits, alongside untreated fabric.⁶ The treated fabrics did not lower odour intensity compared with the untreated ones.⁶ Bacterial numbers on the treated fabric were not significantly lower either, even though the same finish had shown antimicrobial activity in lab tests.⁶

The researchers concluded that “in vitro efficacy does not necessarily predict in vivo efficacy of an antimicrobial treatment”.⁶ In plain words, a finish that kills bacteria in a lab dish may do nothing you would notice on a sweaty body.

Work on two different germ-killing finishes found the same gap: even where the finishes cut bacteria, bacterial counts were not related to differences in odour intensity.¹¹ So the promise behind “anti-odour” clothing, that fewer bacteria means less smell, did not hold up when the fabric was actually worn.

What about skin, and babies?

Skin contact with textiles containing silver is one of the main ways people are exposed to silver nanoparticles.² The advisers also noted that human exposure to silver, through food, hand-to-mouth contact and skin, may be lifelong.⁷ Babies suck their sleeves and their hands, so for them the skin and hand-to-mouth routes come together.

Benn and Westerhoff put the point plainly: “The general public needs to be aware that there are unknown risks associated with the products they buy containing nanomaterials.”¹ Those unknowns are reason enough to leave silver out of a baby’s drawer.

The question nobody has answered

The same summary raises a second worry: bacteria could become resistant to the antibacterial effect of silver in general.² Resistance means germs that survive the very thing meant to kill them, the same problem doctors face with antibiotics. Because silver is also used in medical products, that would matter far beyond the laundry basket.

When the EU’s scientific advisers looked, they found no studies on whether silver nanoparticles help spread resistance and called that “a serious gap of knowledge”.⁷ They said it was “not possible to estimate at this time” whether resistance would increase and spread as silver turned up in more products.⁷

How sure can we be?

Most of this research is a decade or more old, it was done on socks and sportswear fabrics rather than baby clothes, and the only wear trial involved eight men and one fabric. The washing tests show how much silver leaves the fabric; none of them measured how much reaches the skin or a river, or what it does there. So we cannot say these clothes harm anyone, and we cannot say they are harmless.

A modern wear test showing that silver clothing really stays fresher, together with studies showing that silver from fabric neither builds up in skin nor breeds resistant bacteria, would change our view.

What to buy instead

Start with what costs nothing: wash socks and sports kit after each wear, dry them fully, and give shoes a day to air out between wears. Washing removes the sweat that odour-causing bacteria feed on, along with many of the bacteria themselves.

When you shop, skip anything whose tag or product page says “antibacterial”, “antimicrobial”, “anti-odour”, “odour control”, “silver”, “silver ions” or “Ag”. If a listing is vague, one question settles it: “Does this fabric have an antibacterial or anti-odour treatment, and if so, what is it?”

For babies we would go further: choose plain cotton with no finish claim for vests, sleepsuits, socks and bedding, and pass on any baby clothing sold as antibacterial. If a gift arrives with an antibacterial claim, keep it for outer layers rather than next to the skin all night, and wash it before the first wear, since most of the loose silver comes off in that first wash.

For sportswear the same rule applies: pick kit with no antibacterial or odour claim, and wash it after every session.

For adult socks or kit you already own, the studies we found do not show that silver-treated clothing is harmful, and they do not show that it is safe either; if you keep wearing them, wash them as normal. Leave out bleach and oxygen-bleach boosters when you wash them, because bleach speeds up how fast the silver dissolves into the wash water. When they wear out, replace them with plain versions.

So until someone answers the open questions on skin and resistance, plain fabric gives up nothing on smell, and with no silver in it, it has none to wash out into wastewater.