Others claimed it could be positively dangerous, especially when it was fertilised with sewage containing potentially harmful organisms.

BBC: Organic food 'proven' healthier

Professor Philip Marsh, of the Centre for Applied Microbiology and Research, Salisbury, said it should be possible to control the environment in the mouth more effectively to stop the good bacteria being killed off, and to modify the conditions that favour the growth of the harmful organisms.

BBC: Dental bacteria swap resistance

Sure, we understand that all milk must be heat-treated or pasteurized to kill off harmful micro-organisms (in 1987 the FDA mandated pasteurization of all milk products for human consumption).

FORBES: Why Milk Isn't As "Natural" As You Think

"The spread of pathogens on textiles and plastics is a growing concern, especially in healthcare facilities and hotels, which are ideal environments for the proliferation and spread of very harmful micro-organisms, " said Dr Locklin.

BBC: New solution can help 'permanently get rid of germs'

Moreover iron, which gives the planet its characteristic hue, would naturally cling to the varnish, protecting interior organisms from the harmful effects of intense ultraviolet radiation from the sun.

CNN: Researcher: Mars rock varnish hints of life