Hi,
I have 2007 Avalon with 35000 miles, 90% of them are from highway driving. What do you feel about using fuel injector cleaner that could be added to gas? Is there any potential harm form using such products? Thank you for help in the matter.
Chessman
I use Techron. Available at any auto parts store. I know it will cause no harm. I add one bottle per tank about twice a year.
seafoam is also good
is there an actual problem with your injectors? If not, the only harm is to your wallet. Give it an italian tune up and it’ll do the same thing. 
You have absolutely no need for fuel injector cleaner. Major brands of gasoline already contain all the necessary chemicals to keep the injectors like new. But no harm will be done. Try some, if you must, but don’t expect to see a difference in your car’s performance.
You are already using injection cleaner. It is required by the feds (In the US) for all gasoline. There is enough there for almost all cars. There are exceptions and if you have an exception you already know it. If not, don’t try to fix a problem you don’t have.