Can you keep lemon juice on your face overnight?

While this is something you can do (as it's generally not going to cause harm other than potentially drying the skin), it has no benefits, so it's really not a worthwhile activity. It can leave your skin feeling sticky, and the juice will end up on your pillowcase and sheets. Since it doesn't have a benefit, and can increase skin dryness, this seems like a lot of effort (putting it on and cleaning the bed linen) for no real returns. If you do leave it on, be sure it is thoroughly washed off before you head outside, to lessen any risk of reaction with sunlight on your skin.