A primary sign that your grater is dull is that it requires significantly more force to grate ingredients, and instead of cleanly cutting, it mashes or tears the food.
A sharp grater effortlessly slices through food, creating neat shreds or fine zest. When a grater becomes dull, the blades lose their edge. This means you'll need to apply more pressure to achieve the same results. Instead of a clean cut, the food will often be crushed, mashed, or torn, resulting in an uneven texture and a less appealing final product. You might also notice that grating takes longer and becomes more tiring. Observing these changes indicates that the grater's effectiveness has diminished, and it's time to consider a replacement.
Before replacing your grater, try sharpening it! You can often extend the life of your grater by using a honing steel or a specialized grater sharpening tool. However, if sharpening doesn't restore its cutting ability, replacement is the best option for safety and efficiency.