When a large hailstone hits an asphalt shingle, it can tear or even puncture the shingle. But usually, it just knocks granules off the surface. When a shingle loses its protective layer of granules, UV rays from the sun begin to destroy it. More granules fall off around the damaged spot and the bruise grows. The damage may not be obvious at first, so if you suspect hail damage, get an inspection from a roofing contractor. Most offer free hail damage inspections.