Health is not always just about the absence of sickness and disease; it is also about staying safe and avoiding harm. Most electricians have experienced times when they’ve been called to a home where the wiring was not in a safe condition through age or damage by pests such as rodents. Wiring that is in the ceiling cavity is exposed to very high temperatures that help to degrade the covering. That makes it dangerous to your health as it can short out and start a fire.
The same thing can happen when mice or rats chew the wires, especially if they make a nest in the ceiling with bits of paper, dried grass or scraps of cloth, all of which can catch fire quickly from a spark. If you live in an older home, it would be wise to have the electric wires in the ceiling checked out. If they need replacing it is an almost sure bet that the wires in the walls will also be in a bad condition. These too, should be replaced.