I know that when we are talking of hair as a body part, we use it as a singular. But I don't know how we put it into a sentence. Is saying your hair is looking nice correct? And will we say, " Your hair are not looking as good as they used to be", or will we say," Your hair is not looking as good as it used to be". I am kinda confused about it. In a nutshell, can anyone tell me when we use it as a plural and when we don't?