The Vitamin C struggle - Cosmetic Science Talk

The Vitamin C struggle

Hi,
I've been trying to emulate a vitamin C serum with vitamin E and ferulic acid. Quite succesful, but there are some problems.

- I use, just like Paula Begoun, the pure acidic form, L-Ascorbic Acid. 10-15%, with 2-3% Alpha-Tocopherol and 0,5% Ferulic Acid.
First batch I put in an amber bottle with pipette.
Result of stability: I made it about 3 months ago, opening it at least 3 times a week and there still is no change in colour! Amazing... I thought it would discolour in no time.
If I put it on the skin and let is sit for a while, I know there is still active vitamin C left, 'cause I get that annoying metallic smell again, more about that later.
Now that I have airless containers, I want to make the new batch in these by the way.
(The ingredients I use are (maybe too) simple: Aqua, Glycerin, L-Ascorbic Acid, Polysorbate 80, Jojoba Oil, Alpha Tocopherol, Ferulic Acid and a bit of denatured ethanol for the ferulic acid to dissolve and preservatives are benzyl alcohol, benzoïc and sorbic acid.)

The annoying smell. I have read this smelly problem occurs with brands like Mad Hippie and Paula's Choice aswell. All the brands that use the pure form of vitamin C.
I know vitamin C likes to bind with metals. I now have a few questions concerning this:

- The serum smells ok, a typical polysorbate 80 smell. The colour is white.
- If I put it on the skin (at night) and leave it on, within about 15 minutes I sense a metallic smell. If I leave it on for the night and take a shower the next day, the smell is still there.
If I use the serum as a 'mask' and only leave it on for an hour or so, I can get rid of the smell better, but the question is has the vitamin C been transported into the skin very well, or not enough.
I only use it at night. I rinse it off the next morning to avoid having oxidated vitamin C on the skin, which I forgot once and the sheets had yellow/orange stains.

To make a long story short (which isn't possible anymore ;-)
- Does the vitamin C react with metals in or on the skin?
- Does that affect the effectiveness of the serum? Is it a sign of oxidation?
- Is it ok to use it only for an hour or so and rinse it off? The smell really gets in my sheets and it's horrible.
- Is it ok to use sodiumbicarbonate to alter the pH? I make sure the pH is about 3.4. Lower causes irritation. Or does the bicarb make the vitamin C no longer effective?
- Can I use polypropyleenglycol, so that I can lower the amount of glycerin to make it less sticky? Is polypropyleenglycol as bad as they say btw?

Many thanks in advance again!!!

Comments

  • It's not at all a struggle if you use better ingredients. We are about to launch a product and we have none of the problems you mention. But we use a stabilized provitamin C formed from L-ascorbyl 2-phosphate (aqueous Vitamin C) and. L-ascorbyl 6-palmitate. 
    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
  • @Belassi, Is the ascorbyl palmitate just as effective as the pure form? The company I buy the vitamin C from, also sells ascorbyl palmitate. They stated it needs to be heated on very high temperatures, but can it really handle high temperatures? Or can it be dispersed in a serum/cream, instead of really melting it?

  • I don't understand why the company supplying the ascorbyl palmitate states it need to be heated to a very high temperature. Whenever I've used the material it dissolves at well below 100 deg C.

    Be aware that it is oil soluble, however.
  • I feared the ascorbyl palmitate would not be stable enough for temperatures about 120 degrees C., the temperature they adviced ("can't be hot enough or else it won't dissolve"). Strange indeed!
    I'm glad to read it dissolves well below 100.
    1. What carrier would you advice for the ascorbyl palmitate to be dissolved in?
    2. And can I take the same percentage of the palmitate as I do for the L-ascorbic acid? About 5%? Or should I use a higher percentage?
    3. What pH is most suitable for the a.p.? If it is not too acidic, maybe I can add retinyl palmitate aswell?


  • I have never used ascorbyl palmitate for the end uses that you intend and I am thus unable to comment on percentages and such. As the material needs to be dissolved in oil, pH is not applicable.
    I think that magnesium ascorbyl phosphate would be more suitable for your requirements as it is already in use in several commercial products.
  • Ok. Thanks!
    I'm still hoping there are ways to use L-ascorbic acid, since I have about 800 gram of it left. Maybe I can find a formula, I prepare it only for myself so making fresh batches once a week is no problem.
  • I was very impressed with the performance of the test product at 1% usage and we're only waiting for the antioxidant stabiliser to begin production.
    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
  • edited January 7
    Ok, but back to my question, hopefully someone wil answer it:

    • If I use L-ascorbic acid is it ok to adjust the pH with sodiumbicarbonate? It's recommended in many DIY blogs. So just wondering, since it's cheap and available anywhere.
      These are my ingredients: water, L-ascorbic acid (10%), glycerin, jojoba oil, polysorbate 80, alpha tocopherol (2%), ferulic acid (0,5%), denat. ethanol, benzyl alcohol, benzoïc + sorbic acid.
    • The metallic smell? Other people talk about 'meat smell' 'hot dog smell' etc. etc. like I mentioned, this smell occurs in many brands, Paula's Choice, Mad Hippie, Skinceuticals.
      Is it a sign of the ascorbic acid actually oxidizing? Ascorbic acid binding with metals in or on skin?
      Anyone?

    Hopefully I stated the questions right c.q. someone willing to answer the forementioned questions. 
    I have no intention to sell my stuff btw.
  • If I use L-ascorbic acid is it ok to adjust the pH with sodiumbicarbonate?
    - Does sodium ascorbate have any valid benefit to the skin? That is the question you need to ask. If you add a base to an acid you get a salt.
    Is it a sign of the ascorbic acid actually oxidizing? Ascorbic acid binding with metals in or on skin?
    - I really don't know or care, because IMO ascorbic acid is not a stable or useful ingredient.
    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
  • I just read a post of MarkBroussard, giving a formula with L-ascorbic acid and sodium lactate, which gives it with all the other ingredients a pH of 3.5 I'm glad 'cause I just heard from my supplier they will selll sodium lactate aswell.

    It is a useful ingredient for me, because I only make it for myself and can make fresh batches every week. I understand it's different if you want to sell it.
    Getting all kinds of ingredients to stabilize is not worthwile in my case.
  • the firmest conclusion you can draw is that the smell is due to a volatile substance (i.e. has a substantial vapour pressure at room temperature), so it's definitely not ascorbic acid itself or its derivatives

    based on the chemistry of the substances involved, I would guess - and it is only a guess - that it's reacting with the cysteine groups in the proteins on your skin, and generating volatile sulphur compounds which have meaty/metallic odours

    a research paper has described reaction of cysteine with ascorbic acid, generating odoriferous compounds; the researchers used relatively high temperatures, but it's quite possible that small but detectable amounts of these compounds would be generated at skin temperature

    in general there are no free metal ions in the cell (they're transported in proteins known as metal chaperones), so they can't react with anything; also, a reaction with ascorbic acid wouldn't generate volatile by-products
    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
  • @Bill_Toge, thank you so much for this information!

    Would these volatile by-products be potential harmful for the skin? Or are these amounts too small to be harmful?
    And does it make the L-ascorbic acid more or less ineffective, or is it just a small quantity of it that is reacting with L-cysteïne?
  • edited January 8
    I am interested in this discussion on odour being generated by the reaction of ascorbic acid on the skin and it occurs to me that, although ascorbic acid is described as an "acid" it is not so in the definition of carboxylic acid. Ascorbic acid is a ketone (2R)-2-[(1S)-1,2-dihydroxyethyl]-3,4-dihydroxy-2H-furan-5-one that has an acid reaction when dissolved in water.

    I am reminded of the odour formed when dihydroxyacetone (self tan agent) is applied to skin. There is a chemical relationship between dihydroxyacetone 1,3-Dihydroxy-2-propanone and (2R)-2-[(1S)-1,2-dihydroxyethyl]-3,4-dihydroxy-2H-furan-5-one and, both being reducing ketones related to sugars, will react with amino compounds in the Maillard reaction. If you want a quick refresher about Maillard see https://en.wikipedia.org/wiki/Maillard_reaction

    Maillard usually occurs at higher temperatures (cooking temperatures) but the small size of the ascorbic acid molecule and the DHA may well permit a lower temperature reaction. It has been demonstrated that the DHA/skin odour is Maillard - which also explains the tanning or browning activity.

    This might go some way towards explaining the metallic or meaty odours experienced with these ascorbic acid products especially when the high concentration is taken into account.

  • edited January 8
    @johnb, the smell indeed reminded me of self-tanning products. The same stains in the bedsheets (orange/brownish) and a comparable smell!
    Like self-tanning products, the vitamin C serum had the tendency to give the callous parts of the skin (parts of the hands for example) an orange colour. I really have to apply the serum with a glove, or else I will walk around with orange fingers the next day.
    I read a lot of other women also apply these serums containing pure ascorbic acid with gloves because of this. Scrubbing and cleaning the hands thoroughly is not enough to prevent the discoloration.
  • @johnb, in addition to this comment^ 

    So if I get it right, in my case, when I apply the serum:

    • the Maillard reaction takes place like (ketone/reducing sugar related (ascorbic acid) <-> amino acid (L-cysteïne in skin).

    • And although the tempature isn't nearly high enough like in cooking, the small size of the LAA molecule can make it happen at skin tempature, also considering the high amount of LAA.

    • And my question, since I'm an utter nitwit:
    Does it affect the effectiveness of LAA on/in skin? 
    If not, I can't imagine brands like Paula's Choice and Skinceuticals selling it like this?
  • 1. Forget about cysteine as a specific. Other amino acids react similarly.

    2. Yes. It is established that the Maillard reaction is responsible for the DHA colouring effect and it is reasonable to transfer this knowledge to the (structurally) very similar ascorbic acid.

    3. I don't think so. Maillard reaction products usually have very intense colours and odours so the smell you are getting is most likely a tiny side reaction.

  • Thank you very much! :-)
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