There is so much out there about preservatives, it can be overwhelming. And it is such a debated topic. I found this article on the subject of natural preservatives (http://www.botanicalworks.com/NaturalPreservatives.htm) that discusses using some essential oils as preservatives. Now I have to be honest I do not know how effective these have worked since I have never used essential oils as a perservative in my products. I am sure that it may extend the life of the product, but probably not by much. Even if the essential oil has properties you probably have to use so much to make a difference. Then again using too much essential oil can cause skin irritations.
But the best thing to use is a synethic perservative in your waterbased products such as lotions and creams, because it will definately keep your lotion fresh beyond the 1 to 2 weeks with out it.To me it seems that adding a small amount of a synthetic preservative in a lotion or cream recipe is well worth the shelf life. Some of the most common preservatives are Germall® (comes in powder or liquid form) , Germaben II, Optiphen™, and Phenonip which can be found through Lotion Crafter (http://www.lotioncrafter.com/store/Preservatives-c-257.html).
A big concern in perservatives is parabens. There are some preservatives you can purchase that are paraban free. Just check with the manufacturer. If you would like to learn more about parabens, here is a link that that I found that may explain things - http://en.wikipedia.org/wiki/Parabens. On the internet there are many more articles that you can read on this topic.
There are alot of different recipes out there using different preservatives. And I do not know what the author of the recipe chose that particular preservative or if you can subsitute one preservative over another. And if certain preservatives interact with certain carrier oils. But, I did find this link that may help clarify that information- http://home.earthlink.net/~skinesscentuals/Preserve.htm. In addition to that information, here are some more links on perservatives- http://www.craftserver.com/forums/showthread.php?p=199218.
I have also seen some books on making organic body products and the author claims that their lotions creations last a long time (up to 30 days). I would say be very skeptical on these claims. One of the best pieces of advice that was given to me was to test the recipe with the preservative. And then test them with a home test kit. You can purchase a kit from Snowdrift Farms (http://www.snowdriftfarms.com/). But to be certain your products should be challenged tested by a reputable company.
Hope this information clarifies the myths about preservatives. I know the subject can get overwhelming.