Phosphoric acidHydrochloric acid
@Aziz - well, when diluted out in a formula it's perfectly safe. It's like using NaCl as it dissociates in Cl- and H+ ions. The less safe part is during production. But if you are making a batch in a lab you can make a 1% HCl solution and that is fine to use.
My point isWouldn't strong mineral acids like Hydrochloric, phosphoric or sulfuric acids look too harsh on an ingredient label?Even if they're used in tiny amounts, some customers who know no better would get scared just by reading that.Therefore I'm considering acetic acid which is found in vinegar, which some people apply vinegar on their skin.Concentrated acetic acid smells nasty, but we'll see if the finished product does when diluted.
It is meaningless to class acids or bases as "harsh". When used to adjust pH they form harmless salts. Sodium hydroxide and chlorine, suitably combined, product table salt, a key item in our diet.
Freshly prepared aqueous solution has pH of 3.6, changing to 2.5 within 2 hours
@helenhelen OMFAG! I missed your comment! I had not been using this site for some time.
I do not follow what cosmetics gurus do. I already had my fair share of being a mindless sheeple. Justified mindlessness as I was starting out so I must not recreate the wheel. First copy what others do and then modify/improve from there. This is the reason why I made a very good product suited for my skin and weather conditions. My friends are using the same thing as I use, and they said they no commercial ones is as good as mine. Not because they are my friends they lick my backside. It is the power of DIY and countless tests. I live in the tropics and most people here are 'oily', lots of substances used and recommended in temperate countries are too heavy or greasy for us. Skin will "sweat" and shine prematurely even if the weather is cool. (What is solid in a temperature climate is actually liquid in a tropical climate due to temperate difference. Coupled with very high relative humidity. Thus, lots of oily stuff are marvellous over there, horrible over here)
Separate "citric acid" question: Is it ever acceptable to add minute amounts (e.g., 0.05%) of citric acid during the water phase if one knows in advance that the pH will be too high? (It seems like standard practice is to always test the pH and add citric acid during cool down.). Thank you.
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