If you’ve gone multiple days without washing your hair, double shampooing isn’t excessive — it’s essential. Here’s why. Your scalp is living skin . It naturally produces oil to protect your hair. Over a few days, that oil builds up, along with other things! Between washes, your scalp collects: Natural oils Sweat Dead skin cells Styling products Dry shampoo residue Environmental pollutants This combination results in a layer of buildup that sits on the scalp and coats the hair shaft. When you...