The exact extent to which the secrecy and isolation of the wizarding world is maintained varies. Many references are made to the Ministry of Magic performing memory charms to preserve secrecy; however, some Muggles have necessary interactions with the wizarding world. Hermione's parents are Muggles, but have been seen in Diagon Alley. They are fully aware that magic exists, but they forbade Hermione to use magic to fix her teeth (as dentists, they felt that this was cheating). The Dursleys are also aware of the Wizarding World; Petunia Dursley indicates that she learned of it when her sister, Lily, was accepted for Hogwarts. She shared this information with her husband, who is shown to be contemptuous of the wizarding world even before Harry shows up at their doorstep. There is no indication that Dudley was aware of this until Harry is told about Hogwarts.