The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) primarily spreads through respiratory droplets and aerosols released when an infected person coughs, sneezes, or speaks. The confined space of a vehicle creates a unique environment where the risk of transmission involves both airborne particles and contaminated surfaces, known as fomites. The survival time of the virus on interior surfaces is highly variable, depending on the specific material and the extreme environmental conditions a car can generate.
Factors Determining Viral Survival on Car Surfaces
The lifespan of SARS-CoV-2 on car surfaces is dictated by the material’s properties, specifically its porosity and ability to retain moisture. In controlled laboratory settings, non-porous surfaces allow the virus to remain infectious for the longest periods. Surfaces like plastic dashboards, vinyl steering wheels, or metal seat belt buckles are non-porous, and the virus can remain viable on them for up to 72 hours.
Studies on non-porous materials show a virus half-life of approximately four to five hours at \(22^{\circ}\text{C}\) (\(72^{\circ}\text{F}\)). In contrast, porous materials like the fabric found in cloth seats or floor mats tend to dry out viral droplets much faster. This rapid desiccation reduces the viability of the virus, which survives for a shorter duration of 24 to 48 hours on these surfaces.
How the Car Environment Affects SARS-CoV-2 Viability
The extreme thermal and light conditions inside a vehicle drastically alter the baseline survival rates observed in a laboratory. The most significant factor reducing the virus’s longevity on surfaces is thermal inactivation. When a car is parked in direct sunlight, interior temperatures can quickly soar, often exceeding \(60^{\circ}\text{C}\) (\(140^{\circ}\text{F}\)).
Research shows that at \(54.5^{\circ}\text{C}\) (\(130^{\circ}\text{F}\)), the virus’s infectivity decreases by \(90\%\) in just over \(35\) minutes. Even at more moderate temperatures above \(72^{\circ}\text{F}\), common on a sunny day, the virus’s lifespan is significantly shortened to as little as \(5\) to \(30\) minutes. The heat generated by the greenhouse effect in a closed car is highly effective at destroying the SARS-CoV-2 structure.
Direct sunlight also contributes to rapid viral decay through ultraviolet (UV) radiation. The UV light that penetrates the car windows, particularly the UVB component, damages the virus’s genetic material (RNA) and structural proteins. Surfaces that receive direct sun exposure, like the dashboard and seats, will see a much faster inactivation rate than areas shielded from light, such as the floorboards or the glove box interior.
Beyond surface contamination, the risk of aerosol transmission is amplified in the small, closed volume of a passenger cabin, especially during a ride-share or carpool. When windows are closed and the air conditioning is set to recirculate, the concentration of airborne viral particles can build up quickly. This trapped air is the least favorable condition, as particles remain suspended and circulate between occupants.
Practical Steps for Reducing Transmission Risk in Vehicles
The primary method for reducing airborne transmission risk is to maximize the air exchange rate within the cabin. The most effective strategy is cross-ventilation, achieved by opening windows on opposite sides of the vehicle (e.g., front passenger and rear driver-side). This configuration creates a direct airflow path that flushes air out, providing an air exchange rate nearly as high as having all four windows fully open.
When using the car’s climate control system, select the fresh air intake setting instead of the recirculation mode to continuously draw outside air into the cabin. Even cracking windows slightly can significantly improve airflow and reduce the concentration of suspended aerosols compared to a fully closed cabin.
Routine cleaning of high-touch surfaces is an important layer of defense against fomite transmission. Use a disinfectant that is effective against the virus but safe for automotive materials. Solutions containing \(60\%\) to \(90\%\) isopropyl alcohol are widely recommended because they rapidly denature the virus and are safe for most car surfaces, including plastic trim and vinyl. However, specialized leather surfaces and infotainment screens require care.
Harsh chemicals like bleach, hydrogen peroxide, or ammonia-based cleaners should be avoided, as they can cause irreversible damage to upholstery, leather, and plastic coatings. For delicate surfaces like leather, a simple solution of soap and water is often sufficient. Infotainment screens should be cleaned with specialized wipes or a soft cloth dampened with a soap and water mixture to preserve anti-glare coatings.
Maintaining consistent hand hygiene remains a fundamental practice. Washing hands or using hand sanitizer before and after entering the vehicle prevents transferring pathogens to the car’s interior.