hi adrienne;
you got a lot of responses but the issue of CIO is one about which i am passionate, both as a mom and as a former paramedic, so i thought i would throw in my 2 cents; PLEASE NEVER LET YOUR BABY CIO.
it is one thing to allow an older baby, say a 8-10 mo old or older, to cry for 5 minutes or so to kind of break the spell of going to bed crazies, which happens in my house a lot; or to let an even older baby cry for say 10 minutes to get through a tantrum.
but CIO for a 4 month old is extremely dangerous, and frankly, sadistic. a baby that young can not self soothe in any way and all that you do when you let him CIO is panic and possibly choke. babies that young who do fall asleep from CIO are passing out from exhaustion, and that's not part of good sleep cultivation.
babies that young, and i would say up to 8 or 9 months, who are left to cry, can choke, go into respiratory arrest, burst blood vessels, and vomit.
it's very serious. it's a bad idea that has gained traction in our society because parents work excessively hard to make ends meet and are desparate about thier own sleep. also, because it was established by our parents' generation as the way to do things, we are often told that we must do it the same way, even if we know better in our hearts.
my son is 3 and my daughter is 15 months; i put my son's paci back in till he was about 18 months when he became able to either do it himself while asleep, or continue to sleep when it fell out. i do the same for my daughter, usually one to 2 times per night. my son gave up his pacifier about 3 months ago and it was hard for him but he was ready; i knew this because he was chewing the pacifiers to pieces as if they were gum; in other words the pacifier was no longer appropriate for whatever his need was. these days he's into rye bread instead. as for my daughter she's less into her paci than my son and i expect she'll give it up within the year. she doesn't use it except to go to bed and go back to sleep.
in case you're concerned both my unlce and my cousin who are orthodontists say that no damage to the teeth is usually done with pacifiers unless they are used beyong 4 or 5 years old tho my pediatrician feels that pacis outside the house are a notorious source of germs that cause colds. just a thought.
anyway good luck and please be sweet and compassionate to your tiny baby, he needs your help.
with love,
J.