On the scent of sweat Hohenstein Institute optimises textiles with reference to smell

That is reason enough to be concerned with optimising the scent of our garments. Whether the assessment is negative or positive, making scientifically-based sensory judgements about smells emitted by textiles requires both comprehensive instrumental analyses as well as professionally trained human sniffers (sniffers or panelists). Through further development of its odour analysis programme, the Hohenstein Institute has taken a major step closer to achieving its aim of optimising garment odour.

Manufacturers of clothing worn close to the skin (e.g. sporting attire or outdoor wear, underwear or socks), work wear, personal protective clothing and home textiles, as well as shoes and shoe insoles can now, with the help of odour analysis at Hohenstein, focus their efforts on improving the smell of their products and use data gathered to co-ordinate fibre types, construction characteristics and special finishings to reduce unpleasant odours. The head of the Institute for Hygiene and Biotechnology, Prof. Dr. Dirk Höfer, emphasises, “The condition of various materials can be assessed when they are new, as well as after they've been worn, laundered or artificially soiled.” As a result, the processes established at the Hohenstein Institute are not just interesting for textiles designed to reduce odours (antibacterial) or those that emit specific scents (wellness textiles), but also for the laundry detergent and cosmetics' industries for example, because they can be used for precise analysis of the emission of scents. In addition to micro-capsule finishing, laundering as a rule causes fragrances to gather in textiles. Therefore, independent product comparisons and effects of different washing processes can now be assessed with respect to the smell of the textile.

In the past, the Hohenstein Institute has evaluated antibacterial textiles that significantly reduce perspiration odour. This was done with the aid of bacterial perspiration simulation and GC/MS technology in the laboratory. The results were then used to support companies marketing products with antimicrobial effects. For a few weeks now, the scientists at Hohenstein have been in a position to carry out targeted evaluations of textile odours and scents using what is known as an olfactometer – a device to deliver odours to the noses of a group of specially trained test sniffers – in addition to analysis of particular scent molecules using GC/MS. The panelists and devices make it possible to determine precisely the concentration of a smelly substance, its intensity, and make a positive/negative evaluation (hedonic effect) (Image 1). As in the past, when it comes to evaluating smells, the “sensory panel” remains a must. In addition, the scientists at Hohenstein also use a special scent sample release device that directs a standardised volume of the scented air towards the nose of the test sniffer. This is important, for example, during field trials, when garments being worn on the right/left are compared with respect to perspiration odour. In order to take perspiration samples from their point of origin, a special scent sample extractor is used. It is deployed when negative odours must be sampled on-site at a production facility or workplace (e.g. in restaurant kitchens) and carried back to the lab for analysis in order to prevent costly customer refunds.

The Institute for Hygiene and Biotechnology has taken an even closer look at the direct effects sporting garments have on perspiration odour and human skin physiology. First, athletes were equipped with sport shirts of varying moisture permeability (“breatheability”). The breatheability of the garments was determined using the measuring methods developed at Hohenstein, DIN EN 31092 and ISO 11092. Wearing the shirts, the test athletes went through a standardised, intensive work out. Immediately upon their finishing, thermoregulatory micro-circulation data was gathered from the surface of their skin using a thermal imaging camera (thermography).

Image 2 shows the effects of a sport shirt made of cotton (left) compared to a sport shirt with a higher level of breatheability (functional fibres) just after a work out. First, intensified thermoregulatory micro-circulation of the skin and heat distribution, as influenced by the fibre and construction properties of each textile, become apparent. These data were then correlated with skin samples from physiological micro-climates (Image 3). The moisture index of the micro-climate in the underarm before the work out had values of around 60. After athletic activity and perspiration, the moisture index of the cotton shirt climbed well above 100. The differences in the volume of perspiration produced in the underarms were also reflected in the intensity of perspiration odour. The test sniffers at the olfactometer then determined the cotton test swatches placed in athletes' underarms as smelled much more intense and (hedonic) negative in comparison to the textile samples for functional fibres.

For further information on textile odour analysis at the Hohenstein Institute, please contact: Gregor Hohn, e-mail: g.hohn@hohenstein.de