The answer to 'why is my dryer vent pet stains' is that pet hair and dander can accumulate in the dryer vent, causing stains and blockages. This happens when pet hair and dander get drawn into the vent during the drying cycle and build up over time.
Some common symptoms include decreased airflow from the vent, longer drying times, and visible pet hair or stains around the vent opening. To address this, you'll need to clean out the vent to remove the pet hair and dander buildup. This is a task that can usually be done DIY, but if the vent is difficult to access or the blockage is severe, it's best to call a professional dryer vent cleaning service.