I'd discuss that with your therapistI buy them, and never use them because they don't last and i'm afraid i won't have one when i really need it.
I use them to get the snot off the windows it is so much faster than scrubbing with window cleaner. It works great for getting nose smudges off doors too. Does anyone elses dogs try to open interior doors with their noses and leave brown smudges on the door. It's gross and the erasers are about the only thing that gets it off.