Urea cream - gas emission

Hello there!
I have a problem formulating a foot cream and I can't get my mind around what might be causing such a problem.
So basically I'm trying to formulate a foot cream with 15% Urea. As a buffer I am using 9% of Lactic acid pre-neutralised with Sodium hydroxide at a pH 4,5-5,0.
The formula is stable, the buffer works perfectly keeping my pH between the range of 4,5-5,5 but there is a big problem... When the product stays between this certain pH range, huge amount of gas is being produced, which makes the tubes swell up like balloons. I came to the conclusion that this gas is not ammonia because it doesn't smell at all, so I think that most likely it's CO2.
When I tried to start off at a higher pH (5.5) the phenomenon decreased significantly, although it is still visible. But at that case, the buffer didn't work as effectively as it did the first time.

I should add that I was asked to formulate according to an existing product in the market that doesn't seem to have this problem at all.
In the end I found a solution by keeping the product's pH higher than I wanted at first, but I am still curious to know if anyone has come across this kind of problem before.
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Comments

  • Urea is not stable, and during this process will form ammonia and CO2. 
    Once the CO2 is formed, the cream usually looks like cheese with holes  :smile:
    I don't understand how the formula is stable at this point. Anyway, best thing to do (based on my experience is to reduce the amount of water as much as possible and add urea in the last stage of the cream preparation when it is already at room temperature. You should keep ac lactic and the pH around 5.5-6.5
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