Hello @Soona
A few people here will scream at you and will not help you.
If you ask that it means you have no idea what you are dealing with.
Azelaic Acid and Salicylic Acid are automatically considered drugs at that high amount.
I would like to help but… I rather let real chemists/pharmacists here to it.
Basically…It is not easy to answer which is formula is better.
“Better” for me is 3% Salicylic Acid, and approximately 10% Sodium Salicylate (neutralised Salicylic Acid. Near pH 7. No irritation. No soothing agent needed).
Those two formulations are the best for me because I cannot get Azelaic Acid to play with, and I dislike the odour of Sulphur.
I take Urea, for instance, as I have pretty rich experience playing with it. Some people say less than 5% is moisturising, above 5% is exfoliating. Some people say 3% is more than enough to hydrate skin. Whatever they say, I test/ed it out, on myself. Because what people say can be very different from what happens to me. 40% Urea does not exfoliate me, maybe I already have perfect skin. LMAO! 2% to 10% is not hydrating.
It is difficult to one-size-fits-all, in other words. What your application is, and whatnot. As with 40% Urea, very high amount of Salicylic Acid at 10% (not neutralised; very low pH) does not exfoliate my skin. Even the combination of very high amount of Urea and Salicylic Acid do not act as chemical peel on me. Because I have not much ‘dead skin’ to observe the typical result that people are talking about.