[Product question] Affordable retinol? Has anyone tried the iherb creams? Paula's Choice is $65 in Australia :(

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Does anyone know anythign about the retinol creams on iherb, eg this one is only $7 http://au.iherb.com/Madre-Labs-Retinol-Serum-1-1-oz-28-g/56333Does it need to be a certain pH to work? Does it degrade in a tub like vitamin c would?(I already checked Ausskincare, nothing)
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