Yes, putting knives in the dishwasher can potentially blunt them over time. The dishwasher's high temperatures, harsh detergents, and the tumbling action of the dishwasher can cause the blades of the knives to bump against other objects or surfaces, leading to dulling or chipping of the edges.
The combination of heat, water, and abrasive detergents can also accelerate the corrosion process, especially if the knives are made of carbon steel. Additionally, the prolonged exposure to the moist environment inside the dishwasher can promote rust formation, which can further damage the blades.
To maintain the sharpness and overall quality of your knives, it is generally recommended to hand wash them instead of using the dishwasher. By hand washing, you can control the cleaning process, ensure gentle handling, and avoid exposing the knives to the harsh conditions inside the dishwasher.