Is slight glasses fogging always indicative of leaking

I’m wearing a 3m aura, which is a mask that I passed a DIY fit test in previously (it’s new straight out of the package, so the issue is not that it’s too old) and I’m noticing some fogging in my glasses, specifically when I breathe more heavily. Does fogging 100% mean I have a leak or can it just be that the warmth of my breath is still causing fogging? It’s very slight/doesn’t stay fogged after more than a second.