Introduction: Nails are one of the organs which have activity throughout human life. Topical 2% minoxidil has been shown to accelerate nail development by being applied topically on the nails. However, the main mechanism to such effect remains unknown. Moreover, the appropriate preparation and concentration of minoxidil still have not yet been identified. It has been postulated that the higher concentration of minoxidil could accelerate the nail growth more than the 2%, lower concentration.

Objectives: To compare the efficacy and safety of fingernail growth rate between topical 5% minoxidil solution and topical 2% minoxidil solution.

Methods: Thirty participants were randomized into 3 groups: 2% minoxidil, 5% minoxidil, and placebo. Each group of participants was instructed to apply the solution twice daily on the 2nd and 4th finger on both hands. Nail lengths were measured at weeks 4 and 8 by using a digital caliper. Possible side effects were assessed by a dermatologist.

Results: The mean nail growth rate of the 2% minoxidil application (3.32 ± 0.63 mm) was greater than the 5% minoxidil application (2.88 ± 0.50 mm) and placebo (2.87 ± 0.08 mm) at week 8 (p-value = 0.002). No cutaneous or systemic side effects were observed.

Conclusions: In conclusion, 2% topical minoxidil has shown to stimulate a greater nail growth rate than the 5% topical minoxidil solution. Therefore, 2% topical minoxidil is an adequate concentration for effectively accelerating nail growth rate, without any side effects.