Rats exposed to electromagnetic fields produce a cloud of toxic gas around their bodies, claim researchers.
There is debate over power line safety
The finding, in the journal Bioelectromagnetics, casts suspicion on the safety of home and office ionisers.
The rats were placed in cages next to such machines - and concentrations of ozone around their bodies rose beyond recommended levels.
The US researchers say that charged particles from the ionisers may react with water in human cells and tissues.
The finding may also have some relevance to the debate over the safety of power lines - which can also generate an electromagnetic field, albeit of a far lesser intensity at ground level.
Ozone - a gas with three oxygen atoms as opposed to the two in oxygen gas - used to be regarded as perhaps beneficial to humans, but over recent years has emerged as a potential health threat.
If experienced in sufficient concentrations, it can cause shortness of breath and inflammation in the lungs.
Ionisers themselves produce small quantities of ozone in addition to a stream of negatively-charged ions.
The devices have become hugely popular in recent years, particularly in the US, as advocates say that the negatively-charged particles can reduce levels of dust and pollutants in a room - and actually have a directly beneficial physical effect.
The US experiments, carried out at the Pacific Northwest Laboratory in Washington State, involved animals being left directly alongside the negative ion machine, which generates a powerful electromagnetic field in the immediate area around it.
When levels of ozone lingering around the animals were measured, they were found in some instances to be far higher than expected.
In some cases, the levels exceeded those recommended as healthy by US authorities.
Researcher Dr Steve Goheen said that it could be an interaction between the magnetic field created near the ioniser and the water found naturally in the body of the rat.
When rats were removed from the cages, the ozone levels dropped away - but a tray of electrically "grounded" water in the cage was enough to send them soaring again.
"Our bodies, of course, are mostly grounded water," said Dr Goheen.
He said there was no particular reason to believe a human exposed to a similar field would not produce their own personal ozone cloud as well.
What is uncertain is whether long-term exposure to fields of much lower concentration is enough to produce a health effect.
The exposures used in the experiment are much higher than those experienced in homes even directly underneath power lines.
The studies have yet to be reproduced elsewhere, but offer those convinced that electromagnetic fields can harm health a possible mechanism for this.
Other studies have focused on the possibility that electromagnetic fields may encourage higher concentrations of pollutants to gather in houses directly under their path.
The National Radiological Protection Board - the scientific body advising government on this issue - is preparing to issue a report looking into this theory.
However, Dr Michael Clark from the NRPB said that the ozone hypothesis was a new one - and deserved further investigation.
He told the BBC: "This is a recognised research team and people should look closely at their work.
"We would obviously expect this research to be replicated at some point."