Water content plays an essential role in human keratinized tissues such as hair and nails. However, daily routines impair the keratin structure of hair and nails. inducing a decrease in their water content. A new methodology for the determination of the internal and external water content of keratinized tissues was optimized. The water content of untreated human hair and nails was studied. Results showed differences in the water content between hair fibers and nails. Furthermore, hair and nails were subjected to a number of treatments and the water content was determined. Evaluation of the moisture content in treated hairs showed that chemical treatments damaged hair fibers, resulting in a pronounced decrease in their external water content. However, the chemical treatments of nails impaired their integrity and led to a decrease in the internal water content. (C) 2009 Elsevier B.V. All rights reserved.