Introduction Pitted keratolysis is a common skin disease, caused by various gram-positive bacteria including Corynebacterium species, Kytococcus sedentarius, Dermophilus congolensis and Actinomyces species. These bacteria create small tunnels in the stratum corneum, causing pitted lesions at plantar areas. This condition is frequent accompanied by feet malodor and is commonly found in young male adults, especially in soldiers, miners and athletes. The reported prevalence of pitted keratolysis among naval cadets in Thailand was 38.7%. Predisposing factors related to pitted keratolysis are pedal hyperhidrosis and prolonged feet occlusion. Although this condition is generally not painful, our previous study in 2018 revealed adversely affects patients' quality of life.

Regarding treatment modalities of pitted keratolysis, various medications and life-style modification have been recommended. Previous studies revealed efficacy of topical choices, including benzoyl peroxide gel, clindamycin-benzoyl peroxide gel, glycopyrrolate cream,9 erythromycin gel, clindamycin solution, chlorhexidine scrub4 and mupirocin ointment. Oral antibiotics and botulinum toxin injection were also beneficial in pitted keratolysis. As to life-style modification, wearing cotton socks and opened footwear, and proper hygiene, have also been suggested.

Topical benzoyl peroxide is an over-the-counter drug and is known as off-label medication for pitted keratolysis. It has both aerobic and anaerobic antibacterial properties due to inhibition of various cell functions and the response against bacteria is dose related.15 In addition to antibacterial property, benzoyl peroxide can cause keratolysis. Previous studies by Vlahovic et al. (2009) and Balic et al. (2018) demonstrated efficacy of combination of 1% clindamycin and 5% benzoyl peroxide gel in pitted keratolysis. However, study of efficacy of topical benzoyl peroxide alone or comparison between 2.5% and 5% benzoyl peroxide gel for the treatment of pitted keratolysis is currently limited.

Objective The present study aimed to study the efficacy of topical 2.5% benzoyl peroxide, compared to 5% benzoyl peroxide in treatment of unpleasant foot odor, which was considered as major problem related to pitted keratolysis.

Material and Methods First-year naval rating cadets, who had pedal malodor were invited to enroll in this study. The cadets who previously received any topical treatment including topical antibiotic, antiperspirant or aluminum chloride within 6 months prior to the study were excluded. Consent was informed and obtained from all participants. Participants were assessed for behavioral risk factors and level of foot odor measured by a self-assessed visual analogue scale (VAS), using questionnaires. Clinically examination of feet was done in all subjects by treatment-blinded dermatologists. Subjects were randomly assigned either 2.5% benzoyl peroxide gel or 5% benzoyl peroxide gel for 2 weeks. Benzoyl peroxide gel in this study comprised benzoyl peroxide in a gel base. During the study, using of other topical treatment such as topical antibiotics, antiperspirant or aluminum chloride was not allowed. Participants were advised to apply the drug on their both soles once per day before bedtime to leave it on and were able to regularly participate in physical military training during the study. Two weeks after the treatment, clinical examinations by dermatologists and the cadets' self-assessment questionnaires, including feet odor by using VAS, treatment satisfaction and adverse effects, were used to evaluate the effectiveness. Pitted lesions improvement at plantar areas, evaluated by dermatologists, was divided into no improvement, slight improvement (decrease of pitted lesions at feet for 1 level) and much improvement (decrease of pitted lesions at feet for at least 2 level). Data were analyzed using PASW Statistics version 18 (SPSS, Inc., Chicago, IL, USA). Duration of study: 3 months Study design: Randomized control trial