Hair Damage 378 analysis of gases from thermal degradation of keratin waste by thermogravimetry analysis coupled with FTIR and mass spectroscopy, TG-FTIR/MSD has shown ammonia formation, as well as that of other gases, at temperatures below 200°C. The keratin wastes (wool, hair and feathers) have a similar degradation behavior in thermogravimetric measurements, with mass loss steps occurring below 120°C (corresponding to the loss of adsorbed water), and at ~150°C up to ~600°C, accompanied by ammonia release. The yellowing of keratin fibers represents another important aspect of thermally induced degradation. The phenomenon is significant from a cosmetic scientist’s point of view, since hair yellowing is commonly perceived as undesirable, especially in the discoloration of unpigmented gray hair. Several papers have been published on this topic, but the mechanism of color formation has not yet been firmly established. Decomposition of cysteine and tyrosine, and oxidation of tryptophan to kynurenine were proposed as likely pathways for the formation of yellow-colored chromophores. In the case of thermal degradation, the process of yellowing is accelerated at alkaline pH levels and can be controlled by acidic conditions. This can be observed in Figure 5, which shows examples of hair subjected to temperatures up to 200°C for a few seconds. Temperatures Above 200°C Denaturation: Above 200°C the intermediate filaments (IF) in keratins begin to be thermally denaturated. Proteins are macromolecules (polypeptides) with complex structures that are important to their underlying function. This structure can have numerous confirmations–often described as primary, secondary, tertiary, and quaternary. The primary structure is associated with the covalent bonds between atoms that make up the protein molecule the secondary structures involve primarily hydrogen bonding between the atoms (although some disulfide bonding can also occur). These create the well-known alpha helix and beta sheet structures, whereas the ultimate 3D folded structure of a whole globular protein is called the tertiary structure and is important to protein functionality. The quaternary structure usually