What I have heard is that comfrey does not cause any PA issues topically due to the pathway in the liver that would have to be involved to cause an issue.  My husband and I use comfrey oil or salve a lot, sometimes daily or through the day as needed. Comfrey is pretty much a go to in most of my salves I would say.

I think you should be fine using a topical salve that has comfrey in it long term. If you want to be careful though, take a day off every week or two

I just made some for my sister and myself and have been using it for a few days.  I believe Doctor Jones said topically, there are no issues with taking it.

I make comfrey salve and there is no issues with using it longterm.  If you went through doc’s lesson on comfrey, he talks about the study done and it was copious amounts of comfrey given to 6 week old rats. So as he puts it…don’t give it to 6 week old rats at 30 times the dosage! Fun aside, I use it topically on a regular basis for back pain.

I think the risk of exposure to PAs is so low that I wouldn’t worry about it. Not a bad idea to take a break occasionally, but the risks of topical herbs are nowhere near what the internal risks may be.