I think some people have had or have a fungal infection. There are fungi that are airborne. But I'm not convinced it is the root cause of many people's ongoing problems. Some people may have a bacterial infection as well.
For background, I've treated my lips with Clotrimazole and Nystatin liquid, as well as several natural anti-fungal oils. I also successfully resolved a Candida overgrowth with no major effect.