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Tue Sep 04, 2007 11:16 am  |
Virtually ANY cosmetic formula that contains inherently "unstable" oils should remain refrigerated. Unstable oils by definition are oils that have greater than 5% polyunsaturated fats. In chemical terms that means that they have more than one double bond between carbon atoms. When oxygen hits these types of fats it reacts at the double bonds, essentially cutting the original fat into smaller parts. These smaller parts are usually aldehydes and ketones and these type of small chain materials "stink", or smell bad. In a nutshell, I have just defined how an oil becomes "rancid". Therefore, if you buy products that contain oils of this type and leave them open, especially in warmer conditions, that product will begin to smell bad in a rather short period of time.
Now, you can look up oils on google.com and attempt to get a fatty acid composition if you are not sure about products that you have.
Here is a quick reference list of some inherently unstable oils:
Safflower
Apricot
Mink
Sesame Seed
Almond
Avocado
Rice Bran
Wheat Germ
Canola
Grape Seed
Borage
Evening Primrose
Olive Oil
Soy
Mango
Hemp Seed Oil
Flax Seed Oil
Emu
For further reference, here is a brief list of very stable oils that have a practically indefinite shelf life and will not smell or turn rancid:
Coconut
Castor
Macadamia Oil
High Oleic Sunflower Oil
Babassu Oil
Jojoba Oil
Squalane
John |
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President and Chief Formulator for "Never Over The Hill Cosmetics" |
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Wed Sep 05, 2007 8:48 am |
ginnielizz, I have to think that there is something else wrong with a sample of castor oil that is supposedly going "rancid". Castor Oil, by it's chemical composition is not succeptible to going rancid at all. It is over 90% ricinoleic acid which has 18 carbon atoms and only 1 double bond between the carbons. It is NOT a polyunsaturated fatty acid compound and therefore is very stable. We've run OSI tests (oxidative stability) on various castor oil samples. The test is very harsh. The sample is heated to 110C and oxygen is bubbled through it at the same time. It still resists all oxidation for a very, very long time, thus verifying it's stability.
Perhaps the grade of castor oil might be the reason. I would prefer that you use something like CasChem's line of "Crystal" castor oils. These products are highly pure, and castor oil is one of the only triglyceride oils that approaches a "pure compound".
I have to think that maybe the sample you are referring to is contaminated in some way. Other than it's natural "scent" which is quite unique, castor oil should never smell "rancid".
John |
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President and Chief Formulator for "Never Over The Hill Cosmetics" |
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