It is generally stated that drinking plenty of water has a positive influence on skin condition. However, there is no published scientific study that has investigated this matter. The aim of our exploratory 'before-after' study was to evaluate the in vivo influence of drinking more than 2 L of mineral water or ordinary tap water per day on skin physiology. Ninety-three healthy subjects were included in our prospective study. After an initial run-in phase of 2 weeks to monitor individual drinking habits, subjects had to drink 2.25 L day(-1) of either mineral water (n = 53) or tap water (n = 40) for 4 weeks. Bioengineering in vivo measurements on the volar forearm included sonographic evaluation of skin thickness and density, determination of skin surface pH, assessment of skin surface morphology, and measurement of finger circumference. Eighty-six subjects completed the study. In the mineral water group measurements revealed a statistically significant decrease in skin density. Skin thickness increased slightly, albeit not at a statistically significant level. However, when separately analysing those individuals from the mineral water group, who had routinely drunken comparably little before the start of the study, their skin thickness increased at a statistically significant level. Skin surface pH remained almost unchanged in the physiologically optimal range. In the tap water group, skin density increased significantly, while skin thickness decreased significantly. Skin surface pH decreased at a statistically significant level. While in the mineral water group finger circumference decreased significantly, measurements in the tap water group revealed a statistically significant increase. Objective skin surface morphology did not change in any group. In summary, drinking more than 2 L of water per day can have a significant impact on skin physiology. The exact effects within the skin seem to differ depending on the nature of the water ingested. Randomized, controlled, double-blind follow-up trials are warranted to confirm the findings of our exploratory pilot study.

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 ≤ 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 armpit 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.