Some people like to apply the AHA in spots where they need it and then put BP on top. I use BP as just a spot treatment so I usually put on the AHA first and then BP where I need it. But you can put BP first, let it dry and then put AHA all over because AHA can be substituted for your moisturiser - in fact it's better and will leave your skin feeling so soft!

But don't start off using just AHA. Make sure you mix 1/2 AHA and 1/2 of your moisturiser to start, or even 1/4 AHA if you have sensitive skin. Then slowly up the dosage until you can do all AHA. Your skin might burn/tingle a bit when you first use it (it is an acid after all) so you have to be careful. If your skin isn't adjusted to it, high amounts of AHA could 'burn' your skin. I fast-tracked the dosages the first time i used it and literally the left side of my face was raw because the AHA had peeled off so much of the skin.