This can restrict breathing, leading to a suffocation hazard. (momtricks.com)
This could lead to suffocation risks and, in a less serious outcome, will at least make it more difficult for you to keep your baby cool at night. (abckidsinc.com)
Add to that the fact that if the collar is loose or the clothing is too large, the collar can slip up over the baby's mouth and nose, which could possibly lead to suffocation. (babygaga.com)