This study employs a novel method, gas sorption (1), to quantify the porosity characteristics of hair by determining total pore volume, adsorption pore-size distribution, and the surface area of damaged hair. Damage mechanisms were studied by comparing the different pore volume and surface area resulting from two different types of damage: chemical and UV. Hair color measurement and tensile strength, both reflecting the changes in hair cortex, were also employed in this study. The results suggest that hair damage caused by oxidative bleach and UV oxidation follows different pathways. Chemical damage (oxidative bleach) nearly triples the hair surface area in the first minute of bleaching due to the increase in the number of pores, followed by a sudden drop after 10 min of bleaching from smaller pores breaking down into larger ones. In contrast, UV damage shows an immediate loss in surface area in the first 200 hr of exposure and a gradual increase as exposure time continues.