With chemical burns, there is the greater risk of ingestion of that chemical, mostly it is going to be household chemicals that you normally keep well away. But cats, in particular, can be very curious. They will go into cupboards, they will look at things, they will lick things to try and taste them. And also if they do get anything on themselves and dogs and cats are very clean animals and so they will automatically try and lick that off and therefore ingest that potentially caustic and toxin into their bodies.
So the immediate response that you will find it in their mouths so you may get swelling up of the tongue. The signs you will see is irritation, probably drooling. They may go and open their mouths because they are uncomfortable, they may be sick, trying to bring it back up again. And in those cases, if you can have a look in their mouth and see if there is anything that you could remove if there was something that had a toxin on it that you could then take out, you may want to get some water and flush out the mouth if possible. In most cases, I would say the animal probably would not let you do that but if you can then flushing out the mouth would be a good thing to do.
If you find any burns on their skin that they have been licking, try and prevent that from happening either by covering that or in some cases you may have a Buster collar accessible. Or the plastic lampshades, you can put that on your dog or cat to prevent them from persistently licking out the area that you may be concerned about while you are transporting them to a vet.