itchy heels

Every night when I go to bed, both of my heels start to itch.
This itching is waking me up at night as well.
There is no redness, swelling, or anything else out of the ordinary.
During the day, my heels are fine.
I don’t wear socks to bed, but if I do, it is worse.
I have changed my sheets and it still happens.
What could this be??