I air dry my hair most days, and my hair is somewhere between straight and wavy. My hair is manageable, except for the ends. They tend to curl up, while the rest of my hair falls nicely. I'm wondering what might be causing this. My hair is shoulder length, color treated (highlights), and I use a leave in serum containing some silicones and oils. I wrap my hair up in a turban style towel for a while before taking it down to detangle with a wide tooth comb. At this point, I add the serum. Any ideas as to why my ends curl up?