The best "cure" I've ever heard about for getting rid of any smell in a car is using an ozone generator. Using it correctly will get rid of all the smells in your car. It will also help with mold control and removal. You want to be careful using it, though, as breathing the ozone is hard on the lungs. After using it, you need to allow the car to air out for a while before you drive it again. (Full credit on this goes to YouTuber Samcrac for the suggestion.)
As far as there being harmful substances in the smell, I believe they are right, as mold spores can cause you respiratory issues. Getting rid of not only the smell, but whatever is causing it is a good idea. Sitting in an enclosed space with it only concentrates it and you'll breath more than just a lungfull, that's for sure.