The purpose of our study was to evaluate the axillary skin surface pH and explore potential gender-related differences together with the influence of a washing procedure in healthy subjects. After a run-in period, the skin surface pH was measured in vivo in 10 men and 10 women under standardized conditions in three distinct locations of each axilla (at baseline and up to 6 h after washing). Potential interfering influences were thoroughly excluded. Our study revealed a statistically significant difference in axillary skin surface pH between men and women with more acidic values in females (p < or = 0.001). The baseline axillary pH before washing was 6.58 +/- 0.63 (right) and 6.67 +/- 0.65 (left) in men compared to 5.8 +/- 0.53 (right) and 5.94 +/- 0.62 (left) in women. The difference between the right and left arm-pit was not statistically significant (p > 0.05) in any group. After standardized washing procedures with pure tap water, the mean axillary pH decreased significantly in women at all measurement times [lowest value 60 min after washing: 5.51 +/- 0.7 (right) and 5.64 +/- 0.7 (left)], while it slightly increased in men [highest value 240 min after washing: 6.7 +/- 0.59 (right) and 6.78 +/- 0.69 (left)]. In summary, there is a gender difference in axillary skin surface pH. Washing with water further increased the difference between male and female pH values.