My almost 4 month old has this rash under the crease of his neck. I don't know if it's cause his…

mine gets that under his neck but not as bad, but the reason it happens to mine is because drool, formula , or spit up gets there and causes friction. so we just put baby powder there to try and keep it dry. that's what my sister in law told me to do

Oh that makes sense he's teething so he's been drooling a lot

My son always got a rash in his neck fold because milk would drop down it and I thought I would wipe it all off but I didn't. I started wiping him down every night with a wet wash cloth and some soap and putting lotion on his neck during the day and it never happened again.

It's a drool rash. Just wash and dry the area really well after feeding/bathing/excessive drooling.

Thanks ladies!