If you use dryer sheets the wax builds up on the vent. Take your dryer vent and run water over it, you will be surprised, water will sit in the vent, but the vent looks clear. Take an old toothbrush or any kind of brush, and scrub it with soap and hot water, let dry, and in 30 seconds or less you have a very clean filter. Clogged dryer vents are a leading cause of house fires, and dryer heating elements going out. Add a few years to your dryer, scrub that filter.