Peppermint oil is used by exterminators to rid buildings of mice and rats. Saturating cotton balls and batting then stuffing into holes and corners will drive them away from the smell that is offensive to them.
Menthol is the primary component of peppermint oil that brings on a physical reaction when inhaled or rubbed on the skin. The scent is too strong for rodents and bugs and harms their membranes.
The main ingredient of candles is wax. Very little oil is used in making a candle so the scent is only present when the lighted wick melts a portion of the wax. A candle is designed to have a subtle scent and not be overbearing.
Candles do not have enough oil to penetrate the senses of mice or insects. It is recommended by exterminators to use straight oil on a non-evaporating fabric, such as cotton balls, placed in the path of varmints, to chase away from the area.