Temporal Effects of Commercial Deodorants on Underarm Skin pH: A Comparative Analysis

The natural pH of axillary (underarm) skin ranges from 4.5 to 5.5, creating an acidic barrier that regulates the skin microbiome. Modern deodorants often utilize specific pH levels to control odor, yet the efficacy and longevity of these products under different physiological conditions remain understudied. This study evaluated through single-participant comparative analysis how commercial deodorants with varying pH levels alter axillary skin pH over time in both resting and perspiring states. Five stick and cream deodorants ranging from highly acidic to alkaline (pH 3.14 to 6.70) were applied to a single participant in separate trials. Axillary pH was measured before, 30 minutes after, and 60 minutes after application under two distinct conditions: a “non-sweaty” environment and a “sweaty” environment induced by a 15-minute cardio session. In non-sweaty conditions, four out of five deodorants significantly altered skin pH relative to the control at 30 and 60 minutes (p < 0.05). Acidic deodorants lowered skin pH, while the alkaline cream raised it. Strong, significant positive correlations were observed between deodorant pH and post-application skin pH in both non-sweaty (R^2 = 0.9376$, p = 0.0185) and sweaty conditions (R^2 = 0.9161, p = 0.0289). However, perspiration notably reduced longevity; acidic formulations showed a distinct trend toward returning to baseline pH by the 60-minute mark, whereas the alkaline cream maintained its effect. Deodorant pH strongly predicts immediate skin pH alterations. However, perspiration significantly diminishes the longevity of acidic stick deodorants compared to alkaline cream formulations.