My interior dash dimmer switch would not turn off

When I turned on the headlights. What would cause the switch not to work? Turned on the car and the headlights, and the interior lights(dome lights) came on as well, I tried to turn them off by the dimmer switch and it did not work? What would cause that? and would I need a new dimmer switch? Or could this be a recall? The Suv has a 110000kms Thanks Laurel