There are several reasons why outside windows may constantly appear dirty. One common factor is exposure to the elements. Dust, pollen, and other airborne particles can accumulate on windows, especially in areas with high pollution or windy conditions. Rainwater can leave streaks and mineral deposits on windows if it contains impurities. Additionally, nearby trees or plants can shed leaves, sap, or pollen onto the windows, making them look dirty. In some cases, improper cleaning techniques or the use of dirty tools can contribute to streaks and smudges. Regular maintenance, such as regular cleaning and keeping surrounding areas clean, can help minimize the buildup and keep your outside windows looking cleaner for longer.