an information obtained from the XRD data,
suggests that the imposed treatments have resulted in the splitting of larger semi-crys- talline domains into smaller ones having more closely packed polymer chains. Quantitative assessment of hair photodamage with and without application of sunscreen products is an important input to cos- metic chemist for product development and evaluation. However, the task has not been easy due to the complexity of the situation. Hence, often a combination of analytical methods each giving specific information is needed for a comprehensive evaluation. How- ever, most of the available analytical methods index the damage to the cuticle, while the damage to the inner mass (cortex), partic- ularly at the molecular level, remains largely not investigated. From this angle, the positron method utilizes positronium as its de- fect probe, which due to its small size (2 Å) and penetrability can directly characterize the microstructural damage to the cortex re- gion. This special feature of PALS technique, exploited in this study, could be the basis for an important and unique method of product testing and evaluation in the cosmetic industry.