If you're using a Revlon brush that's giving off a burning smell, there are a few possible explanations. The most likely cause is that the brush's heating element is malfunctioning and getting too hot. This can happen if the brush isn't being used properly, if it's been damaged, or if it's simply reached the end of its lifespan and needs to be replaced.
Another possibility is that something is caught in the brush's bristles or in the base of the unit where the heating element is located. Something like a hair tie or small piece of jewelry could easily get wrapped around the bristles and start to melt when heated, giving off that burning smell. If you suspect this is the case, carefully check the bristles and base of your brush for any foreign objects before continuing to use it.
If your Revlon brush starts to give off a burning smell, stop using it immediately and unplug it from any power source. Once it has cooled down, inspect it for damage or any objects caught in its bristles or base. If everything looks clear, try using the brush again following all manufacturer instructions carefully. If the problem persists, contact Revlon customer service for further assistance or take your brush back to where you purchased it for a refund or replacement.