This Surprising (And Common) Mistake Can Cause Greasy Hair, Experts Say

As far as detangling goes, it all boils down to hair type. Those with straight or wavy tresses typically run a brush through dry strands, while those with curls likely don't detangle every single day—and when they do, it's in the shower, under a glob of conditioner. It's not a perfect science, but that's generally what the pros recommend. 

Your scalp produces tons of natural oils—this is a good thing, as sebum is what keeps your strands shiny and moisturized. It's when your scalp accrues too much oil that becomes a slight issue, buildup, flakes, and greasy hair not too far behind. The specific time stamp looks different for each person, but for straight-to-wavy hair types (think pin-straight to loose bends), the hair tends to get oily faster, as it's easy for sebum to travel from root to shaft (it's also why people with this hair type may need to shampoo more often). 

Here's where your brush of choice comes into play: Brushing speeds up the travel quite a bit—the bristles can transfer the oil from the scalp down to the strands. "Brushing your hair while it is dry or running your fingers through your hair moves the oil down the hair shaft, which can make hair look more oily," says hairstylist Franck Izquierdo, co-founder of IGK Hair Care. Not to mention, the oils on your fingertips can introduce even more grease to the strands themselves, but that's a whole other discussion. 

If overbrushing is an issue for you, try not to brush your tresses more than once a day. But if you absolutely must—say, you have some unforgiving snags—you might want to only detangle the lengths. Keep away from the roots, where oil production is most prevalent, and you'll avoid transferring the sebum down the hair shaft.   

Also, "Clean your brush regularly, as residue from hair products, and the oil from your hair, can build up on your brush and then make its way back to your hair," notes Rubin. (Find exactly how to clean those bristles here.)