Final answer:
If a vent brush is missing a protective tip, it's best to stop using it and replace it with a new one to avoid damaging hair.
Step-by-step explanation:
If your vent brush is missing one of its protective tips, you should stop using the brush altogether. Continuing to use a vent brush without a protective tip can cause hair damage from the sharp edges where the tip used to be.
While you might be able to find a replacement protective tip, it's often not easy to match the exact size and shape for the brush you have. Therefore, to prevent any potential damage and maintain proper hair health, it's best to replace the brush with a new one that has all protective tips intact.