Experts have warned against the use of disinfectant tunnels, which many countries are setting up to spray on people as they enter certain premises.

The idea is for people to walk through these tunnels or chambers and be disinfected to reduce the risk of them spreading Covid-19.

However, the experts say these tunnels not only do not help to curb the spread of the coronavirus, but could also cause harm to people using them.

A report in the British-based Occupational Medicine journal warned: "A chemical may be safe when applied topically in liquid form, but extremely toxic when atomised and inhaled."

It studied a range of nine disinfectants commonly used in such tunnels, and said: "Direct aerosol contact with the cornea can cause irritation and irreversible damage. Skin irritation and damage are also common."

It added that the aerosolised particles are easily inhaled into the lungs and "can react with the mucosal lining (such as the inner lining of mouth and nose) causing irritation, swelling and ulceration in the respiratory tract. Some chemicals can be absorbed through the mucosa into the bloodstream and affect distant organ systems, eg. central nervous system and gastrointestinal tract".

If ultraviolet radiation is used - and 15 minute exposure is needed to kill the virus - it "can cause damage to the eye and skin and is a known cause of skin cancer", the article said.

Furthermore, clothes that have been sprayed causes prolonged skin exposure - "until and unless the contaminated clothing is removed, and the skin thoroughly irrigated".

Dr Kristen Coleman of the Duke-NUS Medical School said that while she can appreciate the efforts to design innovative methods to safeguard the public against Covid-19 as countries and states reopen, "human disinfection chambers are not the answer as they pose extreme health and safety risks".

The expert in bioaerosol research added: "Chemical disinfectants are designed to deactivate microorganisms outside of the human body, but the disinfectants are toxic to humans if not used properly.

"Exposure to a surrounding mist of chemical disinfectants through direct contact and inhalation can cause damage to the skin, eyes, and respiratory system."

Professor Dale Fisher, a senior infectious diseases consultant at the National University Hospital said there is no evidence that such walk-through tunnels are at all effective.

Even if they do disinfect a person's clothes and skin, they would not prevent someone who has Covid-19 from spreading the disease once he or she has gone into the building.

Prof Fisher said that the coronavirus is inside an infected person, rather than on the clothes they wear: "The virus does not waft along the street contaminating clothes."

But there is potential danger to people. He said: "No one has exposed humans or animals to disinfectants designed for environmental cleaning over the longer term."

He cautioned that exposure to such "disinfection" several times a day for months may raise potentially inflammatory conditions and cancers.