Pacifiers

AB

I understand that pacifiers help reduce the risk of SID so I have been trying to get my baby to take one but he never did. Tonight he started putting him thumb in his mouth so I gave him a pacifier and he took it! Then when I put him down to sleep he spit it back out. To reduce SID he would have to have it in his mouth when he sleeps ? Does your baby spit it out when he or she sleeps?