According to the U.S. Consumer Product Safety Commission, more than 15,000 fires are sparked every year by clothes dryers.  Lint and other debris can build up in your dryer vent, reducing air flow to the dryer, backing up dryer exhaust gases, creating a fire hazard. The dryer is designed to exhaust the heat and the moisture while it's drying. If that heat and moisture cannot get out of the dryer, then the dryer just sits there and keeps working itself but it can't accomplish the drying. That means the dryer works harder and heat builds up and that is what can lead to a dryer vent fire.  The U.S. Fire Administration recommends regular professional cleaning in order to reduce the risk of fire.