The skin is the largest organ of the body and is designed to keep out contaminants not let them in. Medical patches use specially designed synthetic compounds to go through the skin. It has been shown that those oils that do have penetrative affects are also those that are likely to be sensitisers or irritants thereby showing that the skin is working in stopping contaminents getting through the skin. Using oils in baths is a simple, effective and pleasant way to relax and receive the therapeutic effects. Take care with plastic baths as some oils may cause staining.
All essential oils are antiseptic and evaporate easily, so they make very good air-fresheners.
There are many vaporisers on the market, from the simple bowl of water on the radiator with a few drops of oil on the surface, to vaporiser light bulb rings and specially made vaporiser bowls which sit above candle holders. I personally believe that vaporising rings on light bulbs should be used cautiously, though I have not heard off anyone having a fire through using one. Try experimenting with different combinations, which can be mixed with a carrier oil or non-fragrant alcohol. Because essential oils are affected by sunlight they should be sold and stored in dark glass bottles, with stoppered caps. Make sure that the cap is on securely and the bottle stored up-right in a cool dark place.