Bathroom exhaust fan lint is a huge fire hazard! Exhaust fans can be found in most homes and many businesses. The purpose being to help prevent steamed mirrors, moist walls, and foggy windows. It also comes in handy in when you need to get rid of a not so wonderful smell. However, if these vents are not properly and routinely cleaned they can become dangerous. Just like all types of fans, vent fans collect dust or lint. This lint can cause the motor to overheat and ignite the plastic fan and the wood structure.
These vents are not designed to last forever and it typically tends to be the last thing a homeowner thinks about replacing. Newer vent fans have thermal protection that causes the motor to shut off if they seize and overheat. This type of vent has only been around since the late 70's so there are still millions of older builds that are without this vent safety precaution.
You should clean your bathroom exhaust fan twice a year. If it starts to make noise or has an odd odor than it is time to replace it.