SARS-CoV-2 transmission occurs primarily through the inhalation of respiratory droplets and aerosols released when an infected person coughs, sneezes, or talks. Many people worry about fomite transmission, the spread of the virus through contact with contaminated surfaces. A common concern centers on personal items that regularly contact the mouth, such as a toothbrush. This leads to questions about the risk of auto-inoculation—re-introducing the virus during an active infection—or reinfection from their own hygiene tools after recovery. Understanding viral viability on these materials provides context for assessing this risk.
Viral Survival on Oral Hygiene Tools
Studies have examined SARS-CoV-2 stability on various materials, offering insight into how long the virus could survive on a toothbrush. The handle is typically plastic, a non-porous surface where the infectious virus has been shown to remain viable for up to 72 hours under laboratory conditions. The nylon bristles are a porous material, which generally supports less viral survival than non-porous surfaces because they draw moisture away from viral particles.
The viability of the virus is affected by environmental factors, particularly temperature and humidity. Higher temperatures and air-drying rapidly reduce the infectious viral load. For instance, the median half-life of the virus on plastic surfaces is estimated to be around 6.8 hours. This means the amount of viable virus is cut in half every seven hours. The humid, warm environment of a bathroom, while potentially supporting survival initially, is subject to air-drying, which causes a steady and rapid reduction in infectious viral particles.
Assessing the Risk of Self-Inoculation
The risk of self-inoculation or reinfection from a toothbrush is considered low by public health experts, largely due to the rapid decay of the infectious virus. When researchers test surfaces, they often detect viral RNA, which is merely the genetic blueprint of the virus and can linger for days or even weeks. Detecting RNA does not equate to finding a virus capable of causing an infection. The infectious, or viable, virus is necessary to transmit the illness, and this degrades much faster once outside the host.
For a toothbrush to cause self-inoculation, a sufficient viral load would need to survive the process of rinsing and air-drying, transfer back into the mouth during the next brushing session, and then overcome the existing immune response. The amount of viable virus transferred from a surface to a person’s hand, and then to a mucous membrane, is lower than the amount needed for a respiratory infection. Quantitative risk assessments estimate that the probability of SARS-CoV-2 infection is less than one in 10,000, confirming that fomite-based self-transmission is not a primary concern. The body is already battling the infection during the illness period, and the small, decaying viral remnants on a toothbrush are unlikely to overcome the immune system a second time or prolong the current sickness.
Practical Steps for Oral Hygiene During Illness
While the risk of reinfection is minimal, proactive hygiene steps can reduce theoretical exposure and provide reassurance. If you have COVID-19, isolate your toothbrush from those belonging to other household members. This prevents cross-contamination, especially if toothbrushes are stored together in a single cup or holder.
After each use, rinse the toothbrush thoroughly under hot running water to remove viral particles and allow it to air-dry fully in an upright position. Allowing the bristles to dry completely discourages the growth of microorganisms, including residual viral matter. A common recommendation is to replace your toothbrush or the head of an electric brush once you have recovered and your symptoms have resolved. This ensures that lingering contaminants are removed from your hygiene routine.
Another measure to enhance bathroom hygiene is to close the toilet lid before flushing. This prevents aerosolized water droplets from settling on nearby surfaces, including your toothbrush.