Styling products can leave residue on your hair and scalp. If it's left on there for too long, it can cause dryness, flakes, itchiness, and even eventually thinning. It's best to wash your hair every 2-3 days if you're using a lot of product or at least twice a week. Ideally, use pH balanced shampoos or one made specifically for your hair type to keep your scalp healthy.