Babies can do all sorts of things without understanding. Sometimes babies will scratch their faces with their tiny nails as they touch their faces and sleep at night. The last thing you want is a baby with a face full of little scratches so it's your job to prevent them from injuring themselves. All you have to do is a take a few precautions.
Clip your baby's nails with specialized baby clippers. It is often easier to do this when the baby is asleep. Clip the nails once or twice each week so they stay nice and short. Be very careful not to clip them too short though as it will cause your baby discomfort and they may try to bite their fingers and actually end up hurting themselves. After clipping your baby's nails, smooth out any rough edges with an emery board.
Put mittens on the baby's hands after cutting his fingernails. There are several kinds of lightweight cotton mittens that will cover their hands and thus prevent them from being able to scratch themselves.
Swaddle your baby before sleep. Swaddling mimics the womb and holds a baby's hands down at her sides in a tight cloth that wraps all the way around the body. It's not only good and comforting for your baby, but it also prevents her from touching her face and scratching herself. The American Academy of Pediatrics has issued precautions for safe swaddling. Do not swaddle your baby past the age of 2 months, to prevent her from accidentally rolling over. Swaddle with the blanket loose over the hips and legs to prevent injury. Prevent overheating by dressing your baby lightly. Check on your baby frequently while she's swaddled.
Watch your baby to see if they tend to touch their face or not so you know when you can stop these techniques.
Don't use anything too bulky that the baby might suffocate with.