Can simple daily steam inhalation prevent COVID infection?
Having a lipid coat, SARS COV-2 is heat sensitive and rapidly loses viability/infectivity at 56°C in 15 minutes (10000 units per 15 minutes) and then rapidly losing thereafter (>3 log10) becoming completely non-viable at 70°C.
Likewise, higher relative humidity (>95% at 38°C) also makes it un-infective. It is also inactivated by ultraviolet light, alkaline (pH >12), or acidic (pH <3) conditions. Thus, steam inhalation seems a logical solution to COVID infection. As per timelines (check the figure above), coronavirus remains and proliferates in the nasopharynx and upper respiratory tract for up to two weeks after exposure and is thus amenable to the application of steam.
Therefore, steam inhalation may be especially useful in stage1 and stage 2 of the disease; high concentration of virus in the oropharynx in asymptomatic stage and high viral loads in the upper respiratory tract during early disease states. It might be of only a limited value in advanced disease infecting the lower respiratory tract.
Heated, humidified air has long been used by people with the common cold. GPs in Europe (Netherlands & UK) and the US often recommend it, and it is even included as a recommendation in guidelines and patient brochures issued by European & US medical practitioner societies.
The theoretical basis for this recommendation is that steam may help decongested the inflamed mucus membrane of the upper respiratory tract better and may even destroy the cold virus as it does in vitro. Earlier, some trials have reported benefits of heated, humidified air for symptom relief in people with the common cold and only minor adverse events (including discomfort or nasal irritation).
On the other hand, enveloped viruses have very, very definite heat sensitivity, and thus coronavirus which is a lipid-enveloped virus is likely to be more heat-sensitive than other viruses.
Thus, on the balance of logic and evidence and in view of very low side-effects of steam inhalation if done properly, there seems ‘no harm’ in employing this relatively cheap and user-friendly therapy. It is generally recommended for application twice a day (so that the viral colony is unable to develop).