Have a mold problem? Checkout:
https://lookmold.com/detect/materials...

Mold on windows, is caused by excess moisture and comes in various colors. The presence of mold found on windows is typically harmless on non-porous materials such as glass and metal because the mold cannot thrive to create mycotoxins. Mold found on porous surfaces such as wooden window frames can be cause for concern.

Mold growth on windows and surrounding areas could be a problem in certain situations that you need to be aware of.