If you are sworn in you can be prosecuted for perjury if you lie. That's a different statute with different penalties than "making false statements," which is

If you are sworn in you can be prosecuted for perjury if you lie. That's a different statute with different penalties than "making false statements," which is what you get if you lie to Congress while not under oath. Whether or not witnesses must be sworn in vary based on the rules of the particular committee in question, and is often subjectively done.