A method of assessing damage of a fibrous substrate comprises the steps of: (a) providing said fibrous substrate having a length, a root end, and a tip end; (b) providing a means for assessing substrate moisture content; (c) using said means for assessing substrate moisture content to obtain at least a first measured moisture content value for said fibrous substrate at a first position along the length of said fibrous substrate and a second measured moisture content value for said fibrous substrate at a second position along the length of said fibrous substrate; (d) comparing said measured moisture content values with each other to obtain a measured moisture content differential; and (e) correlating said measured moisture content differential to a substrate damage value for said fibrous substrate. A method of treating a fibrous substrate comprises the steps of: (a) assessing damage of the fibrous substrate according to the method described above to obtain a correlated substrate damage value for the fibrous substrate; (b) using the correlated substrate damage value to select at least one appropriate substrate treatment composition; and (c) applying the appropriate substrate treatment composition to the fibrous substrate.