I applied to the tops of my feet but there was a little left so I used that on the bottom of my feet too. Last night I tried on the side of my knees but it didn't work so well for me.

I do know the skin is thicker on the bottom of the feet and harder to absorb lotions. However, I had such good luck the 1st night I'd probably repeat the same areas again next time.

It's really an individual decision. Whatever or wherever works for you. There's no one right answer in my opinion.