It will not harm anything, what it does do is bead up rain in smaller droplets that the wind can blow away. Those talking of nasty streaks over time probably do not clean their wiper edges. Bugs and small bits of anything sticky that hits your wipers has to be cleaned off occasionally.

Does Rain-X wear off?

Depending on prevailing weather conditions, the Rain-X treatment in your windshield will last for up to 3 months. In my experience, the treatment wears off in a month in rainy weather, but it does tend to last longer in the summer (when there’s less rain… … Rain-X is formulated using silicone-based materials.

How often do you need to apply Rain-X?

Depending on the amount of driving and how often the wiper blades are used, Rain-X can last from 2-3 weeks to several months before a new application is necessary.