Neem oil is a natural product derived from the seeds and fruit of the evergreen neem tree. It is used in over a hundred pesticide products and has important applications in organic farming and medicines. It has been used as a pesticide for hundreds of years and is considered to be safe (1).
These days, neem oil is being touted as a natural alternative to synthetic preservatives.
Neem oil is a mixture of components and not a pure essential oil. Azadirachtin is the active component responsible for repelling and killing pests. The remaining components include fatty acids, essential oils, and other substances. Components of neem oil can also be found in other products such as toothpaste, cosmetics, soaps, pet shampoos, supplements, and medicine.
Most cosmetics include water as an ingredient (for emulsifying); therefore, preservatives are needed to prevent spoilage and the growth of bacteria.
If you have ever purchased an all-natural, preservative-free beauty product such as a face cream and discovered a “funky smell” before it was completely used up it means the product spoiled (i.e., contaminated by yeast, mold, bacteria or fungi). Unfortunately, these products produce natural sugars in a moist environment–the perfect breeding ground (complete with food source) for multiplying microbes. A product can look and smell just fine and still be contaminated. If the product is truly all-natural and preservative-free, it needs to be treated like food: made fresh in small batches and refrigerated (and remember, they will expire).
Products made with natural preservatives fair a bit better in terms of shelf life if used within 30 days after opening, but you might want to ask the question: how good are natural preservatives vs. synthetic preservatives at controlling and killing off any invaders to protect your product (and you)? Therefore, while there are effective, naturally derived preservatives, some can be weakened by exposure to air and water and thus cannot provide the same broad spectrum protection as synthetic preservatives.
Neem Oil as a Natural Preservative
When neem oil is used as a preservative, it functions as an antiseptic, anti-fungal, anti-bacterial, anti-viral, and anti-parasitic. Sounds pretty good, doesn’t it? And it’s used as a pesticide so it must be effective, right? (Although I doubt that argument would work in favor of synthetic preservatives!) Neem oil is effective at keeping oils from going rancid, but it doesn’t do as well protecting the product from bacteria and yeast because it is not a broad spectrum preservative. And it doesn’t seem to like water either. Bad news for technical managers and natural health promoters who want neem oil used as a preservative in water-containing cosmetics instead of the much more effective (and therefore safer) synthetic preservatives available for this purpose, such as Neolone 950. Strict regulations require such preservatives in order to kill all common pathogens. (See http://personalcaretruth.com/2010/06/why-cosmetics-need-preservatives/ for an excellent article on this matter.)
The half-life of neem oil in water is somewhere between one hour and four days. “Half-life” means that the concentration decreases by 50% in …