The answer to 'why is my window greasy' is that windows can become greasy or dirty for a few common reasons. Grease and grime can build up on windows from cooking oils, smoke, dirt, and other airborne contaminants over time. This can leave a hazy, streaky appearance on the glass.
Some common causes of greasy windows include cooking fumes, cigarette smoke, automotive exhaust, and even skin oils from touching the glass. Symptoms include a cloudy, hard-to-clean appearance and difficulty seeing through the windows clearly.