High-grade essential oils are the most efficient killers of microorganisms (for more information see The Aromatherapy Bible: The Definitive Guide to Using Essential Oils, The Complete Book Of Essential Oils or The Illustrated Encyclopedia Of Essential Oils). Basically, essential oils are great disinfectants, and they are also healthy to inhale. They have other beneficial effects on the body and mind. Surround yourself with Eucalyptus during the winter for example, to kill airborne microorganisms. The most efficient way of dispersing an essential oil is to use a nebulizer. Burners and other diffusion methods do not create super-fine particles of the oil. There’s a much greater chance of these particles coming into contact with mold spores, germs, and other airborne bacteria.
A good glass-based nebulizer is made by Young Living. The nebulizer has a small pump which funnels and disperses the oil using a glass chamber but without using heat. This retains the therapeutic benefits of the oil. Other non-heating diffusers and nebulizers are also good, as long as they do not using plastic parts that may contaminate the diffused material.
Many people have bad impressions of aromatic substances. Mostly this is because they are accustomed to inhaling inferior or synthetic versions of essential oils. Look for organic essential oils or hydrosols from a trustworthy source. A good vendor is Mountain Rose, for example.