Do Wool-Blend Socks Smell Different After a Summer Workday?

After a summer workday in leather shoes, does sock material make a difference to odor? A 2023 study compared three types of socks worn by seven men during their normal working days.

Two types containing 58% or 76% wool had lower odor-sensor readings and lower human ratings of odor intensity than socks made mainly of polyester. They also yielded fewer bacteria when recovered fabric was cultured and colonies counted. The study combined three perspectives: an instrument, the human nose, and bacterial counts.

Examining socks worn during real working days

Iitsuka and colleagues aimed to evaluate the deodorizing and antibacterial performance of business socks with different wool contents under conditions close to everyday wear. Moving beyond conventional tests in which a single odor compound is adsorbed inside a bag, they focused on the mixture of many compounds encountered in actual use.

The participants were seven men in their thirties to sixties who usually wore business socks and leather shoes and worked mainly at desks. Testing took place from late July to early August 2022, on three closely spaced days when each man did his normal work.

Participants put on the socks at home before commuting, and the socks were collected at work about eight hours later. By wearing different sock types on opposite feet, the researchers sought to make conditions such as weather and activity as comparable as possible on each day.

The three types differed in more than wool content

The comparison included sock P, made of 98% polyester and 2% polyurethane; sock W, made of 76% wool, 21% polyester, and 3% polyurethane; and sock D, made of 58% wool, 40% polyester, and 2% polyurethane. All were conventional rounded-toe socks.

Importantly, the polyurethane in D had a deodorizing treatment. W and D therefore differed not only in wool content but also in treatment. Their thickness and mass per unit area were similar, but not identical.

The left/right combinations were P/W, W/D, and D/P, with the order of these combinations randomized for each participant. This design meant that each person wore all three types on both the left and right foot. The analysis treated left and right samples as separate data and included sample type and participant as factors. Multiple worn samples did not mean that the number of participants had increased.

Measuring with a sensor, the human nose, and culture

The foot sections of the collected socks were cut out. Some fabric was used for bacterial counts, and the remainder was placed in bottles for odor measurement. The sensor drew in gas that had accumulated inside each sealed bottle and recorded the response of a semiconductor sensor.

For sensory evaluation, three assessors were selected each time from a panel of ten women in their twenties. The same three assessed both socks from the same wearer on the same day. They used both a 0–10 odor-intensity scale and a direct comparison between left and right samples.

To count bacteria, small pieces taken near the front of the sole were immersed in liquid to extract microbes, which were then cultured on medium at 37°C for 48 hours. The resulting colonies were counted. The 48 hours refers to incubation time, not to wearing the same socks for 48 hours.

The two wool blends had weaker odors

The mean sensor reading was about 350 for polyester-dominant P, compared with about 260 for wool blends W and D. Both were significantly lower than P. These numbers are instrument readings, not units of odor-molecule concentration or the intensity directly perceived by a person.

Human assessors also judged W and D to smell weaker than P. The strength of statistical evidence differed between ratings on the scale and direct comparisons of two samples, but the overall direction agreed.

There was no significant difference between W and D in either sensor readings or sensory evaluations. This means no difference was detected under these conditions, not that 58% and 76% wool necessarily perform identically or that 58% is the minimum required content.

There were fewer culturable bacteria, but their relationship to odor was not simple

Mean colony counts were approximately 39,000 per square centimeter for P, 26,000 for W, and 24,000 for D. Both wool blends had significantly fewer colonies than P, with no significant difference between W and D.

Sensor readings and human intensity ratings were positively correlated, with a correlation coefficient of 0.55. Sensor readings and colony counts also had a positive correlation, at 0.38. Across samples, stronger odor tended to accompany higher bacterial counts.

The correspondence was not perfect, however. Sensor readings alone cannot yet be used to determine bacterial counts or human perceptions precisely. Nor does this correlation establish that having more bacteria directly caused the odor differences in this study. Bacterial species and individual odor compounds were not measured.

How wool may work, and what remains to be tested

The authors discussed the possibility that wool takes up odor compounds because of its moisture-related and chemical properties. Interactions with acidic and basic compounds, for example, are a mechanism suggested by previous research. However, this wear trial did not directly analyze which molecules were adsorbed or in what quantities.

Because D had a deodorizing treatment, it remains possible that this compensated for its lower wool content. Even at the same percentage, a thinner and lighter sock contains a different actual amount of wool per foot. The authors identified a need to consider fabric quantity and construction as well as fiber percentages.

The study involved seven men during normal summer workdays, without fully standardizing footwear or living conditions. Broader comparisons covering exercise, other shoes, or repeated laundering remain to be investigated.

Summary

Among three types of business socks worn for about eight hours in summer, the two wool blends had lower sensor readings, human odor-intensity ratings, and cultured colony counts than the polyester-dominant type. Sensor readings were related to both human ratings and bacterial counts, illustrating the value of combining measurement methods.

There was no significant difference between 58% and 76% wool, but the treatments also differed, so an optimal wool content remains undetermined. The study provides a basis for investigating relationships between fabric composition and odor under real wearing conditions.

The paper lists two authors as affiliated with Okamoto Corporation, and a footnote also identifies that company as the first author’s affiliation at publication. No separate funding or conflict-of-interest statement was found in the main text examined.

Reference

Iitsuka N, et al. Verification of the Deodorizing and Antibacterial Performances of Wool-Content Business Socks through Field Experiments. Journal of the Japan Research Association for Textile End-Uses. 2023;64(11):686–691. doi:10.11419/senshoshi.64.11_686.