Paintings are complex structures which begin to deteriorate when the artist puts down the last touch of paint.
While it is normal for paintings to acquire a certain appearance of age, There are avoidable factors, such as humidity and extremes of temperature which can cause serious harm to a painting.
Careless handling causes instant and sometimes major damage.
Avaoid hanging your paintings above a fire or radiator or below water pipes. Damp walls and direct sunlight are also harmful to paintings.