Despite your worries of forming bad habits or your grandma's warning that your child will have braces until they're 25, using a pacifier for your baby can be an actual life saver. They calm your baby in stressful situations, help them sleep better at night, and allow your breast to have a bit of a break if you've turned into a "human pacifier." But is it safe for baby to sleep with a pacifier? Evidence suggests that it's more than just safe. Believe it or not, sleeping with a pacifier may play a part in saving your baby's life.
According to an article in Scientific American, using a pacifier at night and during your baby's nap can decrease your baby's risk of SIDS, or sudden infant death syndrome. Though the correlation between the two or the cause of SIDS isn't known fully, it is thought that sucking prevents your baby from falling too deeply asleep or stopping their breathing. The Mayo Clinic cautions against forcing a pacifier if your baby just won't take one, and making sure to wait at least one month after birth to establish a healthy breastfeeding relationship.
So the short answer is yes, it's safe to let your baby use a pacifier when they sleep. However, like anything, there are a few safety caveats to keep in mind when choosing the best pacifier for your baby.
According to Parent's Guide, ensuring that the pacifier is in good condition — no rips, signs of sear, tears, or breaks in the plastic — will lower the chances of a piece becoming a choking hazard. Similarly, be sure to choose an appropriate size for your baby's age, as they'll outgrow the ones designed for newborns fairly quickly and can choke on it if it's not the correct size.
As far as concerns about habit forming go, simply encouraging your child to stop (slowly or all at once) at an appropriate age will make it a non-issue.