How does shampooing works?
Shampoo traps oils, so if you do it too frequently, you may dry your hair out, leaving it prone to breakage, says Angela Lamb, MD, an assistant professor of dermatology at the Icahn School of Medicine at Mount Sinai in New York City.
“Hair produces natural oil called sebum, and shampoo is an emulsifier that captures and traps excess oil, dirt, and product residue, which you then rinse out to clean the hair,” Lamb says. For the most part, some dirt is ok and natural and you definitely want some oils to remain in your hair.
Starting at the scalp is crucial. If you've ever had a professional shampoo at a salon, you know how much time they spend on your scalp. It's not just an impromptu head massage. Scrubbing the scalp is a key step to an effective shampoo. The magic number for cleansing the scalp is three minutes, no matter your hair length or hair type.
Focusing your initial shampooing efforts on the scalp helps remove dirt, sebum, and build-up that collects there. Spending less than three minutes on your scalp is like quickly running a mop over a dirty floor rather than scrubbing the surface of its grime.
Finally, you should be giving your hair a cold water rinse. If you thought this was a beauty myth repeated over the years in magazines and on websites, this is a beauty do that is actually true. While hot water raises the cuticle and therefore makes products more effective, you need to rinse hair with cold water to close the cuticle. A flatter cuticle has a smoother surface, one which reflects light and makes hair look shinier. It's ok not to if you're afraid of a cold shower, but if you're brave and committed to having shiny hair, then take a chance and move that tap over to cold.