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A Safety and Effectiveness Evaluation of a Callus Softener Containing Potassium Hydroxide

Kevin M. TowleCardno ChemRisk, San Francisco, CA.

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Jordan S. KozalCardno ChemRisk, San Francisco, CA.

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David A. GalbraithCardno ChemRisk, San Francisco, CA.

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Andrew D. MonnotCardno ChemRisk, San Francisco, CA.

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Background: Limited safety information has been described in the peer-reviewed literature for callus-softening products containing potassium hydroxide.

Methods: This pilot human use study evaluated the safety and effectiveness of a commercially available callus softener, containing less than 10% potassium hydroxide by weight. Baseline callused skin was scored (grade 1–4) on each study participant’s feet (n = 10). Participants’ feet were soaked and then a licensed manicurist applied a callus softener product to the right foot, which remained on callused skin for 3 to 5 minutes (no callus softener was applied to the participant’s left foot). Both feet were then wiped with a wet towel, and a foot rasp was used to file the callused skin, beginning on the left foot. Callused skin was scored and participants’ feet were evaluated by a physician immediately after use, 1 day after use, and 1 week after use for the presence or absence of skin irritation, adverse skin reactions, and chemical burns.

Results: No adverse events were reported by study participants or the physician for all evaluation time points. Each participant’s highest callus grade score on the treated foot either improved or remained the same following product use (compared to baseline). Mean callus grade scores were 1.75 at baseline, 1.55 immediately after use, 1.25 1 day after use, and 1.50 1 week after use.

Conclusions: Results from this pilot study suggest that callus-softening products containing less than 10% potassium hydroxide are likely to be safe and effective products under intended use scenarios of 3- to 5-minute application times, as dictated by product label instructions.

Corresponding author: Andrew D. Monnot, PhD, Cardno ChemRisk, 235 Pine St, Ste 2300, San Francisco, CA 941104. (E-mail: andrew.monnot@cardno.com)