The Mona Lisa is showing her age, museum curators in Paris said while announcing a scientific study of the 500-year-old masterpiece.
Leonardo da Vinci painted the Mona Lisa between 1503 and 1506
The thin poplar wood panel around Leonardo da Vinci's painting is showing
signs of warping, causing curators at the Louvre "some worry".
The museum has commissioned a study to evaluate the Mona Lisa's vulnerability to climate changes.
The painting will remain on display during the testing, the Louvre said.
"Its state of preservation is currently the source of some concern," a statement issued by the museum said.
Deterioration in its wood panel was "greater than that which has been
previously observed," it added.
The study, to be conducted by the Centre for Research and Restoration of Museums of France, will better determine what materials the painting is made of.
The painting, whose cryptic smile lures millions of visitors to the Louvre, is displayed behind glass to protect it from climatic changes and camera flashes.
It will be put in a specially renovated room in the Louvre early next year.
The Mona Lisa was painted between 1503-1506 and was thought to be named
after the sitter, most likely the Florentine wife of Francesco del Giocondo.
It moved to France with da Vinci in the early 16th Century, where it has remained except for a short spell when it was stolen in 1911. The painting was discovered two years later in a Florence hotel.