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No more body odour!

They are marketed using terms such as “anti-odour”, “freshness guarantee” or “odour killer”: garments which have been treated with odour-binding or bacteria-inhibiting substances. The manufacturers promise the purchasers of not only sportswear but also suits, socks and shirts that there will be a significant reduction in the build-up of odour caused by perspiration.

How do they work?

We can distinguish here between three completely different operating principles: in textiles with an antimicrobial treatment, the reproduction of the bacteria which feed on particles of skin and sweat is inhibited and this prevents the formation of unpleasant body odour. To make antimicrobial textiles effective, bactericidal chemicals or silver particles are added or applied to the spun fibres. Silver has been used for centuries, for example to disinfect drinking water. The strong, multi-charged silver ions break through the cell walls of the bacteria, causing them to die. Since the start of this century, antimicrobial silver treatments have been used increasingly with textiles. Cutting down the number of bacteria has the effect of reducing the by-products which are produced as perspiration decomposes and which smell so unpleasant. Deodorants work in the same way. However, the purpose of most textiles with an antimicrobial treatment is not to reduce odour but, rather, they are used where hygiene is a top priority, for example in hospitals or the food processing industry.

bomby_reyon_clip_image006 In antimicrobial textiles, the reproduction of the bacteria responsible for unpleasant body odour is inhibited. However, the effectiveness (= dotted line) is confined to the immediate vicinity of the fibre. Picture: Hohenstein Institute

Textiles with a photocatalytic treatment, whereby contaminating organic particles are broken down by (sun) light, are currently still at the development stage. The idea is that the photocatalytic effect will be achieved by coating the textile fibres with nanoparticles, for example of titanium dioxide (TiO2). These have already been used for some time in cosmetic and textile sunscreening products to provide better UV protection.

How effective are they?

At the Institute for Hygiene and Biotechnology at the Hohenstein Institute in Bönnigheim, the team led by Prof. Dirk Höfer has been working since 2001 on studying the effectiveness and biological safety of various textile anti-odour treatments.

Antimicrobial activity is measured in accordance with recognised standards such as ISO 20743. Treated textiles are compared with untreated samples made of the same type of fibre. The textiles are prepared using a set quantity of test bacteria and kept for a predefined period of time. Then the number of living bacteria on the test sample is compared with the number on the untreated sample.

Tests on silver-based antimicrobial treatments have shown that the effect is limited to a very small radius of 50-100μm, approximately the thickness of one textile fibre. This means that the growth of bacteria on the skin can only be prevented if the treated textile is in very close and direct contact with the skin.

Fabric refreshers such as “Febreze” also make use of the way cyclodextrins work. Here, too, unpleasant odours are, as it were, “captured” in the basket structure of the sugar molecules, thereby neutralising them.

bomby_reyon_clip_image008 In odour-binding textiles, odour particles are trapped by tiny, basket-shaped sugar molecules (cyclodextrins) and only released when the textile is next washed. Picture: Wikipedia

Biological safety

Most of the antimicrobial treatments currently on the market are based on silver. Since the silver ions are bound into the fibre or on the fibre surface, their effect is limited to a small radius around them. The bacteria-inhibiting effect applies primarily to the textile itself and the sweat absorbed in it.

The natural skin flora are normally hardly affected by it at all. Further peace of mind for consumers is provided by tests on skin friendliness which rule out any risk of cell damage or sensitisation to a particular textile.

Cyclodextrins are biodegradable and completely non-toxic and can be permanently attached to natural or synthetic fibres. Since they do not play any role in the process of odour formation, there is no known risk of them causing irritation.

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