Well, the main negative effect is that it can reduce your milk supply. The newer, silicone shields seem to impact less than some of the older types made with various materials, but they can still reduce. They can also be messy and difficult to work with, and some babies are very reluctant to give them up . Overall, it's best if we can figure out how to get you nursing without a shield, but they are very useful tools under the right conditions.

HTH
Jen