Frizzy hair after humid summer weather usually happens because humidity, sweat, chlorine, saltwater, sun exposure, frequent washing, and heat styling can leave hair dry, rough, and more likely to swell. Fix it by shampooing gently, conditioning the lengths, using leave-in conditioner, drying with a microfiber towel or T-shirt, applying a small amount of anti-frizz cream or serum, deep conditioning weekly, reducing heat, and trimming rough ends if needed.