The risks of machine washing hiking boots include the breakdown of materials, loss of waterproofing, and potential deformation of the boot structure. The glues and materials used in hiking boots, such as leather and synthetic fabrics, can react adversely to water and detergents. The heat and tumbling action may weaken glue bonds and cause the boots to lose their shape. Additionally, the waterproofing treatments on the boots can be stripped away, reducing their effectiveness in wet conditions.