Mould growth in washing machines is primarily caused by residual moisture, detergent build-up, and inadequate airflow. Brittany Bailey, a cleaning expert, emphasizes that keeping washing machines mould-free requires just three easy steps. First, after each load, users should wipe down the door and rubber seal to eliminate moisture, particularly around the gasket and drain holes. Second, leaving the washing machine door open for about 30 minutes post-wash allows for proper air circulation, preventing moisture accumulation that fosters mould growth. Finally, users should open or remove the detergent drawer to air it out, as moisture and detergent residues can lead to mould and unpleasant odours. By following these steps, users can significantly extend the lifespan of their washing machines and maintain a fresh-smelling laundry environment.