Ahh, then it is definately an allergy; the moisturizer + foundation provided a thick enough barrier between the product and your skin. Best to stay away from that one, yes.

I only asked about skin prep. because sometimes people put it on a harshly scrubbed, freshly cleaned, bare face thinking "it keeps my face from getting oily to scrub is so throughly." To the contrary, they're surprised when their pores clog up and they break out and get ruddy-faced because they're traumatizing their skin and dumping harsh makeup products onto it. So that's why I asked. Moisturizer OUGHT to be a proper-enough barrier for your skin (unless you're allergic, in which case STAY AWAY from the product).

The other thing that I've found (having EXTREMELY sensitive skin) is that things that might be okay on my body will NOT be okay on my face; the skin of my face is particularly sensitive and delicate. So testing on the arm might work for some people, but not be very accurate for others.