...And I just found a link from Butch's page to some university research from 2004 that indicates that burning candles made with essential oils does help kill bacteria on surfaces in a room.
Very interesting! If I'm reading this correctly, electric low-heat diffusers such as the Scentball (that's the cheapest source I've seen for those) would have the same effect. And which oils you'd use would influence the effectiveness- read the link above for their findings.
The researchers, Dr Lindsey Gaunt and Sabrina Higgins, have discovered that adding essential oils to the candle can destroy bacteria such as Escherichia Coli and Staphylococcus aureus on surfaces. Working with Professor John Hughes in the Bioelectrostatics Research Centre, Lindsey and Sabrina have been testing different essential oils, such as orange, thyme, and eucalyptus, which when dispersed into the air and combined with the ions produced in the candle flame, all have a powerful bactericidal effect.
Where candle use would not be appropriate, for example in a kitchen, the same bactericidal effect can be produced by using plug-in devices combining the appropriate essential oils and ions generated by an electrical discharge.
According to Lindsey Gaunt, the candles and electrical devices could be as effective as liquid disinfectants, together with the added benefit of being able to penetrate porous surfaces and fabrics in a room with very little personal effort.
This unique combination of essential oils and electrical ions has demonstrated a remarkably powerful bactericidal action, with up to nearly 100 per cent bacteria kill.
Remember that essential oils are HIGHLY flammable; don't go dropping them into open flames on candles. Flash fires can happen!