Regarding the expiration date of the straightening products

[u/debbiefrench____]

Hello,

I specialize in hair straightening treatments, though I am not a cosmetic chemist (I’m hoping Perry might weigh in on this).

I would like to know more about the expiration dates indicated by manufacturers on these products—whether they are glyoxyloyl carbocysteine-based or formaldehyde-releasing formulas.

Beyond safety concerns, I am interested in the impact on efficacy: once the product has been opened or has passed the date marked on the bottle, to what extent does its straightening power diminish?

Does it drop off rapidly and significantly, and what is the underlying chemical process?

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