The answer to 'window smells bad' is that the most common causes are mold, mildew, or trapped odors. Windows can develop a musty or unpleasant smell for a few reasons - moisture buildup, decaying organic matter, or trapped pollutants. This is a common problem, especially in bathrooms, kitchens, or damp areas.
If the smell is mild, you may be able to address it with DIY cleaning. Try wiping down the window frame and sill with a solution of warm water and white vinegar. This can help remove mold and mildew. You can also try leaving the window open to air it out. However, if the smell is strong or persistent, it's best to call a professional window cleaning service. They can do a deep clean and identify the root cause to properly resolve the issue.