Cosmetics, especially AHA or BHA peels is not something I would take a chance on. Actives such as Vitamin A ( retinol) and Vitamin C are also highly unstable and should be used as soon as possible.
Remember, strength and efficacy of peels and cosmetic formulations is not only determined by the type of ingredients you use, the percentage of actives, but also the activity or pH.
pH is especially difficult to stabilize and normalize in a cosmetic formulation. If it's old, or worse, has been exposed to too Hight heat or extreme cold temperatures, humidity, change of pressure, or the product is exposed to air, the formula will de-stabilize a lot quicker.
At the very least it is no longer efficacious beyond the expiry date, has gone rancid, or at the worst, the chemical compounds have changed and could cause adverse reactions.
I have worked in the pharmaceutical industry for 7 years, and have had experience with manufacturing of cosmetics, drugs, medicines and nutritional supplements.
Expiry dates should NEVER, ever, be taken lightly.
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