The back pages Almost the last word

摘要

I straighten my hair and my friend curls hers with a heated hair wand. Humidity, sweat or washing instantly reverses the process. My wavy hair goes frizzy in humidity, but her straight hair doesn't. What is happening? Human hairs are hygroscopic, meaning they absorb atmospheric moisture. Stretching wet hair shafts during a drying process sets them into a desired configuration, be that straight or curly. This is fundamental to hairstyling. It is a temporary structural change though, only remaining until moisture is absorbed, whereupon the hair shafts return to their natural state. Certain hair types are more prone to this, such as those with frizzy, finely structured hair shafts. Hair that has undergone thermal or chemical processing, such as relaxing, permanent waving, bleaching or tinting, is also more prone. These processes compromise the structure of each hair's outer protective layer, or cuticle, exacerbating permeability and moisture absorption.