How stable is a "stable" antioxidant serum?

edited December 2016 in Ask the Beauty Brains
Many brands with antioxidant serums or Vitamin C serums use tubes or dropper bottles. It is well known antioxidants, like retinol or ascorbic acid, are extremely sensitive to air. So you would think these products will oxidize, possibly cause skin damage and you should avoid them. Of course the companies claim the products are completely stable. On the internet it is also said a vitamin c derivative is more stable than ascorbic acid. Also an anhydrous Ascorbic Acid product is more stable.

But what does "more stable" or "stable" in general mean? Can you assume the antioxidants didn't oxidize at all after 3 months in a tube or dropper bottle, and after 1 year? If you look at the vitamin C products from The Ordinary, can you really say they are 100% stable? Or will the products oxidize after opening because they are not packaged airless, and you shouldn't use antioxidant products in tubes/dropper bottles?

Comments

  • I personnally bought ascorbic acid in powder that I mixed with water in a dropper bottle. I keep it into my fridge and that's the only way I found to keep vitamine c stable (no oxydation after opening).

    I don't know about the Ordinary stuffs, so I'm curious about the answer
    :D
  • @Peter

    >Can you assume the antioxidants didn't oxidize at all after 3 months in a tube or dropper bottle, and after 1 year? 

    lol i dare you to place it in a hot sun in a car... (i noticed someone's $200 serum just went bad before the expiry date). 

    > If you look at the vitamin C products from The Ordinary, can you really say they are 100% stable? Or will the products oxidize after opening because they are not packaged airless, and you shouldn't use antioxidant products in tubes/dropper bottles?

    TBH yes, there is no 100% in life. at best 99.99%
    Oxidation STARTS when they are opened.

    A founder of a skincare brand explains this and i am re-wording this as i can't remember where i read it. 

    Similar to a Fruit. Once the fruit is cut opened, the vitamins are halved every hour. So i imagine with skincare... say when you first opened the product, 

    for example A 20% Vitamin C serum may be 20% when you opened it, depending on the conditions of oxidation (air,heat,UV,bacteria etc) ... at 6months, that Vitamin C serum will not be 20% anymore. Some of the antioxidants will be used up by then. If you are lucky it is an antioxidant still... not a pro-oxidant.

    From experience. my 4 month old DIY Vitamin C stored in an airless container in the refrigerator was still good. I tested it after 4 months and phew. still usable. It's still in my refrigerator, using it for testing/experimentation to see how long it goes. 


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