[MRM]

It would be unusual to have a growth on the outside of your window. Sometimes you can get growths like lichens that grow on tree bark if you have a warm, moist climate. If you can't scrape it off with a finger, and it's not on the inside, then it is on the inside.

Don't freak out. Mold is indeed everywhere in the local environment and if that is mold in the glass, it came from the same local environment that you live in. This means that you are already exposed to it and it doesn't hurt you. Mold rarely causes health problems unless you have a specific allergy, and even then you need to inhale it or get some on you.

If the growth is on the inside, you have what is called a seal failure. I couldn't make out the seal detail or brand of window, but it looks like a high-end fixed casement from about the mid 1990s. Double pane windows are sealed with a vacuum between the panes. High efficiency windows have argon gas sealed between the panes. Either way, there are a couple of problems that can cause the seal between the panes to break. Then outside air gets in, condensation forms and is trapped, and you get funny stains or growing things.

A seal failure itself is not a big deal. It won't cause further damage to the home or window. It just looks like crap and to some extent you lose the insulation value of the high-E double panes.

Windows of that vintage were notorious for seal failures. The better brands have 10 or 20 year warranties on their glass against seal failures. Look in the corners of the windows and see if there is a manufacturer's mark etched on the glass. It should give you the brand and it might give you the date. Call that company's 1-800 number and see if they'll send you a replacement sash. You'll probably have to install it yourself, but replacing a sash is well within the capabilities of almost any homeowner. At worst, a window repair vendor will charge $50 to $100 to swap out the sash for you.

Let us know what you find as you look at them closer.