It’s no secret that the outside of your vehicle’s windshield can get very dirty, very quickly. Having windshield wipers and fluid in place for on-the-go cleaning definitely helps, but sometimes, the smudges that are making it hard to see are coming from....inside the vehicle.
source https://lifehacker.com/how-to-clean-the-inside-of-your-windshield-even-at-its-1846163421