Nanoparticle technology may take the stink out of smelly feet

Socks coated with zinc oxide nanoparticles (ZnO-NPs), a suitable textile additive, were effective in preventing bromodosis and the development of pitted keratolysis (PK), a Thai study suggests.

“[Bromodosis and PK are] highly prevalent in specific populations – athletes, field workers, miners, and military personnel, [and impair] quality of life (QoL),” said lead author Dr Punyawee Ongsri from the Mahidol University, Bangkok, Thailand, during his presentation at EADV 2020. Over a third (38 percent) of naval cadets in Thailand reportedly have bromodosis and PK. [Military Med 2018;183:e633-e637]

Bromodosis is characterized by malodourous feet secondary to excessive sweating and bacterial overgrowth. [J Invest Dermatol 1986;87:159] In PK, causative organisms* produce proteolytic enzymes that degrade the epidermal keratin, leading to a crateriform appearance in the soles of the feet. Consequently, this produces a compound of thiols, sulphides, and thioesters that give off the unpleasant odour. [Br J Dermatol 2018;179:1220-1221; An Bras Dermatol 2016;91:106-108]

Save foot = save face?

While these may be addressed through good hygiene and topical** and systemic treatments, [J Dermatolog Treat 2019;30:627-629] nanobiotechnology may augment the treatment arsenal and provide lasting antibacterial effect that could help save the afflicted from embarrassment, noted Ongsri.

As such, Ongsri and his team evaluated 148 cadets (mean age 20 years) from the Thai Naval Rating School who were assigned to a 14-day field training course. Cadets must have no history of abnormal foot lesions or malodorous feet. They were randomized 1:1 to wear ZnO-NP-coated or uncoated socks ≥8 hours daily during training. Questionnaires and self-assessments were completed pre- and post-training. Concomitant use of antibiotics, antifungals, antiperspirants, deodorants, or perfumes were disallowed. [EADV 2020, abstract 18]

Compared with baseline, post-training assessment revealed significantly less foot odour among cadets wearing ZnO-NP-coated socks (p=0.009).

Odour-wise, compared with those wearing ZnO-NP-coated socks, more cadets wearing uncoated socks apparently have it worse (14 percent vs 4 percent; p=0.04), rating it as ‘disturbing’. “[The] more intense foot odour had a [significant] effect on their daily life,” said Ongsri.

The uncoated socks also led to a higher incidence of PK compared with the ZnO-NP-coated socks (40 percent vs 16 percent; p=0.05).

Satisfaction-wise, more cadets wearing ZnO-NP-coated socks were highly satisfied compared with those wearing uncoated socks (96 percent vs 84 percent; p=0.01).

From science to first-hand

Evidence has reflected the antibacterial efficacy and skin safety/compatibility of metal*** O-NPs, the most common being silver (Ag) O-NPs. [Master Sci Eng C Mater Bio Appl 2014;44:278-284; Sci Technol Adv Mater 2008;9:035004] However, reports on environmental toxicity have limited the use of AgO-NPs, Ongsri pointed out.

“ZnO-NPs are being used more in the present day [and] have no evidence of environmental toxicity. [However, its efficacy has] only been proven in vitro. Our study is the first in vivo study testing its antibacterial efficacy in the real-life setting,” said Ongsri.

Apart from the science backing the potential of metal O-NPs, Ongsri’s first-hand experience as an intern in the naval medical department drove him to probe deeper into the issue. “I saw a high number of foot infections [among] military personnel. I wanted to find a way to prevent and treat these fungal and bacterial infections and the associated conditions.”

The favourable efficacy, improved QoL, and high level of user satisfaction suggest that ZnO-NP-coated socks may be used as a prophylactic measure for at-risk populations, concluded Ongsri. “These socks could provide a new primary prevention option for … those susceptible to these conditions. We are continuing our research with other textiles and hope to treat and prevent the growth of bacterial and fungal infections.”