Wiper blades degrade from UV exposure, ozone, and physical wear. Rubber compounds harden over 6–12 months and develop cracks that streak the windshield.
Signs of failure: streaking, chattering, missed spots, visible cracks in the rubber edge.
Wet-weather visibility is the safety issue. Worn blades reduce visibility in rain by 40–60% compared to new blades. Hydroplaning risk goes up because you can't see road conditions.
Replace once a year as a habit. Total cost: $20–$40 for quality blades. Worth doing in spring (before summer storm season) or fall (before winter precipitation).
Premium blades (silicone, beam-style) last longer than economy blades and perform better in heavy rain. The price difference ($10–$20) is worth it.