Dress smart and respectful for the Vatican. No sleeveless clothing, shorts, skirts not covering the knee or hats are permitted inside the Vatican. Even if you get past security, you'll be turned away by the door attendants.
2) Don't Touch
It goes without saying that you are not allowed to touch any of the collections inside the Vatican.
While there is a cafeteria in the Vatican for you to have lunch, it is forbidden to consume any food or drink inside the exhibition halls.
While you can take photos inside the Vatican Museums, the use of a flashbulb is forbidden. No photography of any kind is allowed in the Sistine Chapel.
You are also not allowed to use your mobile phone inside the exhibition halls or the Sistine Chapel.