How do you tell when a Frenchie’s skin problem is turning into an infection?

[jinna cameroun]

I’ve been going down a rabbit hole lately trying to understand French Bulldog skin issues better because it seems like a lot of them start as something small, a little redness, a bit of licking, maybe some moisture in a fold, and then turn into something more obvious if the dog keeps scratching or rubbing the same area.

I found one guide that explained the progression pretty clearly, especially the signs to watch for and when it’s probably time to stop guessing and call the vet:
https://brachydogcare.com/french-bulldog-skin-infection/

What I’m wondering is how other Frenchie owners here usually spot the difference between basic irritation, allergies, and an actual infection. Are there any early signs that stood out in your dogs before it got worse?