Hair is composed of proteins, lipids, water, and small amounts of trace 
elements. All proteins in animal and human bodies are built from permutations of 
amino acid molecules in a polypeptide string. The polypeptide chains of protein 
keratin are organized into filaments in hair cells. Hair is one of the most 
difficult proteins to digest or solubilize. Among the most common dissolving 
procedures for hair are acidic, alkaline, and enzymatic hydrolysis. For the 
analysis of hair, the solid samples are transferred by solubilization via 
digestion into a liquid phase. Small molecular solvents and molecules with 
hydrophobic groups appear to have higher affinity for hair. A good solvent 
attacks the disulfide bonds between cystine molecules and hydrates the hair 
shaft. Consequently, the hair becomes a jelly-like mass.