Masks are not created equal; every product has its perfect timing. But, there’s always room to go too much, especially for fine hair. If you leave it overnight despite the suggested time, you may feel heaviness and excess moisture in your hair until the next wash. It cannot damage your hair, but it also won’t do you much of a favor. At the same time, there are masks designed for kinky and curly hair that must be left overnight. In this case, you will need a shower cap and some old clothes.