A man wearing a wig disguised as an old woman in a wheelchair threw cake at the Mona Lisa on Sunday, which smeared the protective glass casing with white cream but left the painting undamaged.
The man pretended to be disabled in order to get a wheelchair and approach the painting, a Louvre Museum spokeswoman told the dpa news agency.
When he was close enough to possibly the world's most famous painting, he threw a hidden cake at the display case, she added.
Immediately after the incident, Louvre security guards were filmed escorting the man out of the museum as he cried in French, "Think of the Earth …There are people who are destroying the Earth."
The Paris prosecutor's office on Monday identified the cake-thrower as a 36-year-old man. He was detained and placed under psychiatric evaluation.
An investigation has been opened into the damage of cultural artifacts.
The Mona Lisa was placed behind a protective case in the 1950s after it was damaged in an acid attack by a vandal.