I had a very annoying verruca (plantar wart) on my foot for several months. Never had one before. I ignored it while travelling and when I got home tried to treat it with with salicylic acid. It didn't help much and made it more painful. My doctor told me that there wasn't really any cure beyond the body healing itself in its own sweet time. My body was was definitely procrastinating.
So, along with using salicylic acid to remove the dead skin, I started dousing it with 100% pure tea tree oil once a day. Presto! The verucca soon abated and disappeared in a few weeks. I assume the tea tree oil has some effect on the body to heal itself.
So if you're stuck with a stubborn verruca, it's worth giving tea tree oil a shot.