By design, which toyota motor sales usa inc. acknowledges, the 2019 4runner sr5 windshield and front window defrost functions with external air only, and will not function with recirculated vehicle cabin air. this exposes vehicle occupants to potentially hazardous external air conditions during winter driving. i've personally been exposed to this health hazard on multiple occasions while operating the 4runner windshield defrost hvac in inclement weather: in heavy freeway traffic and exposed to vehicle exhaust-laden external air, and in mountain winter driving and exposed to external diesel exhaust from snow removal vehicles. as an asthma sufferer such exposure during normal operation of the vehicle is a health risk. on at least one occasion i've experienced significant respiratory distress due to this 2019 toyota 4runner design defect. i'm concerned about continued exposure and related health hazards for me and other vehicle occupants while operating a integral vehicle feature, one that is necessary for safe driving during inclement weather conditions.