I recently received this question and since it is something I have been asked before I thought I would post my answer here. Actually, it's not my answer but one from Dr. Pappas, a brilliant chemist who is renowned for his work with the essential oil industry. Dr. Pappas created Essential Oil University for publishing and sharing his research of the chemical constituents in essential oils and how they affect the body. He also does quality control for the company we purchase our oils from. So here is his answer regarding colored glass:
"Many times we get calls from customers asking us if the oils are OK to store in colorless bottles because they are afraid that light will damage the oils. Unfortunately many people have succumbed to the fear mongering and propaganda put forth by the makers of colored glass when it comes to storing essential oils. The amber glass makers will tell you that amber is best, the green glass makers will tell you that green is best, etc.
"The truth is that most essential oils are photochemically inactive in the visible region and reactive in the ultra-violet (UV) region of the electromagnetic spectrum. Since UV light of high enough energy to cause photochemical reactions in most organic molecules is absorbed (not transmitted) by normal glass, regardless of color, it makes no difference if the oils are in brown, blue, green, purple or whatever color glass."
"Of course there are a few exceptions, like with the chamazulene containing oils (blue chamomile, blue yarrow, blue tansy, etc.) that you would not want to store in colorless bottles for long periods under heavy lighting conditions. This is because chamazulene has strong absorption in the VISIBLE region of the spectrum (thus the intense dark blue color of these oils) and so it is the lower energy visible light and not just UV light that can significantly effect these oils."
"But even so, thermal degradation and reaction with oxygen are the biggest enemies of these blue oils, which is why all of our chamazulene containing oils are refrigerated and stored under nitrogen, maintaining the nice dark blue color when you receive your shipment (many times you will find that other suppliers selling these oils will ship them after they have turned dark green due to oxidation from improper storage). I know many people will still believe they have to keep their oils in drab brown bottles, even after reading this, but I can tell you that based on the research I have done and my experience as a chemist, it makes no difference what color the bottle is for most the oils."
So there you have it. Colored bottles are more expensive than clear and do not allow you to see the quality of the essential oil. So I prefer to use clear bottles for our 1 dram, 2 dram, and 4 dram essential oil.
The back stock of our oils always remains in a closed cabinet so no UV light reaches them at all.
That being said, in the near future we will be changing our 1 oz. spray bottles and dropper bottles over to either blue or amber glass for purely aesthetic purposes.
Kathryn Doran-Fisher is a Traditional Naturopath, Certified GAPS Practitioner and owner of Elder & Sage.