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Pharma said:

Do you have any source for that claim? Sodium and lactate are both electrolytes… Anyway, it does degrade faster in presence of certain metal cations (mostly ‘redox active’ heavy metals).

You are right, I mean metal ions. I’ve never seen a formulation with LAA and Sodium salts together, so I assumed Sodium is also speeds-up the degradation.

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DeedeeUkulele said:

Whenever I add ferulic acid to my anhydrous L-ascorbic acid serum, it quickly turns yellow. I know it’s not the LAA because the solution containing LAA alone is still completely clear after a month.

Serum 1 - Still clear after 30 days
15% LAA
85% propanediol

Serum 2 - Yellow in 5 days
15% LAA
1% ferulic acid
5% Sodium lactate
79% propanediol
* Heated to 50C to dissolve the ferulic acid

The difference between those 2 formulas is not only ferulic acid, but also Sodium lactate. Try to take it out and see what happens. LAA quickly degrades in presence of electrolytes (which is Sodium, right?), although I am not sure if it applies in waterless solutions.

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There is a study called “Mixed solvency approach”, it describes synergy between solvents. There is SA used as a model poorly soluble ingredient. So I guess you are following their method - combine sodium citrate, propylene glycol and polysorbate to get synergy of solvents.

For commenters above: sodium citrate is a hydrotrope used in many products to dissolve SA (or better to prevent recrystallization), it is not used as a chelator here (reference: Application of Sodium Citrate As Hydrotropic Agent In Spectrophotometric Analysis of Salicylic Acid)

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According to “Solubility prediction of salicylic acid in water-ethanol-propylene glycol mixtures using the Jouyban-Acree model” study, solution of 50%/50% water/PG can dissolve 2% SA. So it is more 1:25 ratio. But it for pure SA with low pH.

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Salicylic acid will precipitate with time because 20% of PG is not enough to keep it soluble. Although since you had raised the pH to 3.5 only around  22% of SA are not neutralized, so it can potentially be enough .

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If I am not mistaken the next formula is correct for the ratio:
138.121g of SA + 84.007 of baking soda = 160.11 Sodium Salicylate + other products of the reaction.

I don’t think there is much profit in using sodium citrate if you gonna neutralize SA.

Solubility in glycols is IMHO quite high, it low in water+glycol mixture. According to research called “Solubility prediction of salicylic acid in water-ethanol-propylene glycol mixtures using the Jouyban-Acree model” you need a 50%50% mixture of water+propylene glycol to get 2% solubility of SA 

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It is more complex question then just dissolve oils.
Since the mixture will be apply to shoes you need to test if it leaves marks, ruins the color of fabric, how good it masks odor, how quickly it evaporates etc.
All of the mentioned ingredients may dissolve oils, but my choice would be alcohol since it is a good solvent for essential oils (used in perfumes), evaporates quickly without leaving stains and has sanitizer properties (which is good for shoes since some of the smell comes from bacterias). Cons: could wash off some of the color from fabric, but I think this spray will be used in small quantities.
Other mentioned ingredients don’t have these properties. Polysorbates will leave oily stains. Witch hazel is basically an alcohol. 

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chemicalmatt said:

You need to put octocrylene back into that formula if you want to sell in the USA. That is the indicated stabilizer for avobenzone that is also an approved sunscreen. 

+1 to this statement. Avobenzone is quite unstable and octocrylene is a must to partially stabilize it.

lesmith1018 said:
Hi, 
does anyone have some suggestions for low cost SPF boosters for sunscreen?
thanks!

Not sure what you mean by “boosters”, but I assume you mean stabilization of filters. There is quite good research called “The photochemistry and photostabilization potential of plant extracts on sunscreen absorbers” which shows stability improvements of the sunscreen when some plant extracts are added (e.g. green tea). Check it out and see if it suits your formula.

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mikeylamar said:

That’s very interesting, I didn’t realise that lowering the water content and using glycerin will increase stability. So I assume that vitamin c retains all of its stability in glycols then. 

Check The Ordinary 23% ascorbic acid in propanediol. Just two ingredients, no water - completely stable. Although not comfortable to use - itchy, shiny, grindy.

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MarkBroussard said:

@mikeylamar

 add in 20% Ethoxydiglycol or Propanediol … it will feels much more pleasant on the face.

Cafe33 said:

I am using 10% Propylene Glycol and 20% Ethoxydiglycol 

Correct me If I am wrong, but in Europe we have 2.6% limitation for Ethoxydiglycol in leave-on products

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Disclaimer: I am not a chemist, just DIY enthusiast.

drjayseesunish said:

Preservative? 

Hi! Yes, you should have a broad-spectrum preservative in products which contain (or will be interacting with) water, because water is a source of life and a good ground for bacteria and mold.

drjayseesunish said:

Why we need to preservative because these all are chemicals?

Even more - everything in our life is chemicals. Why? Because bacteria and mold are so stubborn, so they can live and growth in almost any cosmetic product.

drjayseesunish said:

Is phenoxyethanol at 1%  good?

Again, I am not a chemist, but I think just phenoxyethanol is not enough, since most of commercial products tend to not use it solely. Also, preservative choice depends on many factors - how long shelf life should be? should it be “organic” or “natural”? What is pH of your product? etc.
  

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Some sellers say that betaine helps to dissolve allantoin

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Pharma said:

It may. As said, all depends on the context… and your definition of ‘potency’.

I’ll rephrase the question.
Imagine I have a solution of salicylic acid and sodium citrate in water with pH, e.g. 5.0. If I apply this on skin how it will work? As salicylic acid and sodium citrate would work, or as sodium salicylate and citric acidsodium citrate would work?

All I want to understand if salicylic acid looses it properties when dissolving it that way.

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Pharma said:

Mixing salicylic acid with betaine in water results in betaine salicylate (at a pH dependent degree).

Also, mixing salicylic acid with sodium citrate (mono-, di-, or tricitrate doesn’t matter) results in sodium salicylate and citric acid (or a corresponding citrate). Again, the degree depends on pH and molar ratio.

In the end, all that matters is pH which turns salicylic acid into a more or less water soluble salt and thereby allows for easier dissolution. In low % aqueous or even anhydrous preparations wherein salicylic acid is soluble, production of salicylate salts results (for most cosmetic ingredients) in a reduced solubility.

Does it mean that salicylic acid looses it’s potency when dissolving it that way (because now it’s not the acid, but salt)?

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Paprik said

I do wash my hair everyday, but a lot of women do not. Yet, they can still have not-oily hair for days

isn’t it because they have long hair so the sebum evenly spreads? Whereas you, probably, has short hair, so it gets greasy quicker

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Hello, My name is Dima and I am from Ukraine. I am a software developer, but I have an interest in understanding formulations (as a hobby). I am also formulating some simple products for myself (just water-based simple serumstoners, no creams or fancy stuff).

So thank you all for the info provided on the forum and your answers to my questions, I really appreciate this.

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@grapefruit22
I am sorry if my messages look too harsh (as Perry says, it is easy to be misunderstood in text), I didn’t want to attack you in any way. English is not my native language, so I probably use wrong words sometimes and they look offensive, sorry if so.

grapefruit22 said:

You mean all the few you selected were about animals? It’s not true that all or even most of them were such kind of study

If you can provide a study from that list which is relevant - I would really love to discuss it. I found only one done on 4 pieces of human skin and it has a note that results might be irrelevant due to small number of trials.

I also checked the one with hydroquinone and have some doubts on it:
1. Only 16 women. I don’t think math would say it is statistically representative
2. These women were using Vitamin C on one part of the face and hydroquinone on other. They were covering whole face with a SUNSCREEN, So basically the comparison was Ascorbic acid + sunscreen with hydroquinone + sunscreen. How we can be sure it’s ascorbic acid helps but not the sunscreen? There should be 3rd group which is wearing ONLY sunscreen. Although it’s not included because results might be unpleasant (what if just sunscreen gives better results that combination of it with vitamin c or hydroquinone?)
3. Are we sure that brightening effect is based on Vitamin C special properties but not on pH and acidity? Are we sure that any other AHA acid with such percentage rate (15%) and pH value (around 3.5) won’t perform same, better?

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@Perry Agree, but do you think ascorbic acid could oxidize and degrade already in the skin during night or two and give the stain?

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grapefruit22 said:

You can check the mentioned studies and see if they are convincing.

As I said, I already took a quick look at some of the studies mentioned in the article and all of them are done on animals. It is not cool to throw in huge list of studies and say “the truth is somewhere there”. If you have a convincing one - show it, don’t expect people to go through each of them instead of you.

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grapefruit22 said:

The second article had 70 references to publications, none of them was convincing?

Actually, I made a quick glance at studies provided in the article and found none to be  done on humans, most of them are made on animals, which is not convincing.
Could you provide a specific study which is done on statistically meaningful number of humans with well-defined methodology?

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1. You didn’t read my questions carefully. I am not declining the fact that ascorbic acid evens skin tone. Although it seems it doesn’t do it in the way I expect. I expect it to fight hyperpigmentation and reduce dark spots, but it seems ascorbic acid just gives a small shade of fake tan which visually hides the issue rather than treating it.

2. I am talking exclusively about ascorbic acid, not derivatives.

3. I’m not surprised you get instant brightening of the face. Most serums have huge percentage of ascorbic acid, which is white powder. If you put such amount of zinc oxide you would get the same whitness. But in the long run ascorbic acid just stains the skin (IMHO)

4. You can read the same amount of feedbacks from people who say same thing as I do - Vitamin C makes skin orange and just gives a fake tan (which makes skin look even, but it’s only visual effect)