-I want an apple. What about you? I want an apple. What about you?

And you put more emphasis on feelings.

-I feel a little cold. What about you? I feel a little cold, don't you think?

Generally speaking, there is not much difference. In some reference books, say how you are = how you are.

Are used to ask each other's opinions, physical condition and so on. It's just that sometimes oral habits are different.

For example:

You and your classmates are discussing the completion of your graduation thesis. You ask the other person, "Hey, did you pass the graduation thesis?"

"Not yet, just returned by the tutor, saying that the argument is not sufficient?" The other party replied.

"I also returned mine yesterday." And then you suddenly want to ask the other person's boyfriend?

So you can say "What about your BF" (What about your boyfriend? Did he pass? )

Similarly, you can also say "How's your BF" (Well, how's your boyfriend? Did he pass? )

Conclusion: How ≠ How,

So in a way, how are you? How are you.

But in the end, the meaning of these two sentences reached the same goal, both of which were "how to ask each other".

So how are you = how are you.