Dirty dryer vent ductwork will reduce the dryer efficiency.  Over time, the buildup of lint, dirt and other materials may ignite and cause a fire.  Yearly dryer vent cleaning is recommended.

Clothes dryer fires are more common than you might think. The National Fire Protection Association (NFPA) reports that dryers and washing machines cause an average of 15,970 fires each year, with dryers causing 92% of them and an average of $200 million in property damage. Electric dryers are more likely than gas dryers to cause fires due to higher heat discharge from electric dryers which increases the problem of lint buildup.