In vivo measurement of water content of the fingernail and its seasonal change

Background: Recently, there has been increasing awareness regardless keeping nails in good condition. Maintenance of an optimum water level in the nail plate is very important since water content affects the nail condition. However, a simple method for in vivo measurement of water in the nail plate quantitatively has not been reported. In this study, we applied Near infrared spectroscopy (NIR)-based prediction of water content of the cut nail plate to in vivo measurement to obtain information about the seasonal change of water in the fingernail. Methods: Diffused reflectance spectra of the nail plate of the fingernail were collected in the NIR region with an NIR spectrometer in vivo both in summer and winter from the same 15 Japanese female subjects. The water content of the nail plate in vivo was calculated from the NIR spectrum using partial least square regression analysis. Results: It was possible to apply NIR-based prediction of water content of the cut nail plate to in vivo measurement. We also found that the water content of the nail plate varied from person to person but not with the finger of the individual. The average water content of the nail plate was significantly lower in winter than in summer (P < 0.05). In summer, the water content in the double-layered nail tended to be higher than a nail in good condition (P < 0.1) and significantly lower in the split nail (P < 0.05). There was no significant difference between the groups in winter. On the contrary, the amount of water absorption tended to vary depending on the nail condition. A large amount of water was absorbed in the double-layered nail and a small amount in the split nail both in summer and winter. Conclusions: The water content of the nail plate of fingernail was predicted by in vivo measurement using NIR spectrometry. Physiological information of the nail in vivo, such as aging and other disorders could be obtained by this method.