Skin biophysical assessments of four types of soaps by forearm in-use test

While soaps are the most commonly used cleansing agents for human skin, they also damage the epidermal barrier and potentially increase the risk of disorders such as contact dermatitis.

This study set out to compare the potential skin irritancy of four types of soaps and their effects on the skin barrier function and biophysical parameters.

In a nonblinded comparative study, three types of soaps (alkaline, creamy, and glycerin soaps), and a syndet were applied to four different groups of 15 healthy subjects. Subjects washed their left forearm with the respective soap at home at least four times a day for seven days. Biophysical skin parameters, including transepidermal water loss (TEWL), erythema, friction, and pH, were measured at various time points using the Cutometer^® MPA 580.

After the first wash, a significant increase in TEWL was observed for all groups compared to the pre-intervention period. For the alkaline soap, a substantial increase in pH was observed at all time points compared to the baseline. Syndet, the only acidic soap in this study, showed a significant decrease in pH at the last time compared to all time points. The mean value of erythema was significantly higher in alkaline soap users than glycerin and creamy soap users.

Our study showed that alkaline-based soaps could cause erythema and increase TEWL and skin pH due to their strong cleansing action, and the addition of compounds such as glycerin can modify these effects. A newer generation of soap containing a mild surfactant such as syndets causes less skin damage.