Over time, and after doing a lot of sampling and reading, I came to be much better at identifying notes. I've also become more sensitive, so that I don't need to spray much. Now, one or two, rather than three or more sprays is usual for me.
About "skin chemistry:" I've been working with an older female relative on this. My skin seems to be very good for fragrances. It holds them "true" for long periods of time. I think the middle notes are more prominent than they are for most people. My relative doesn't seem to sweat much, and lives in an apartment that has central A/C, but it seems that her skin "eats up" the fragrance, and it doesn't stay true at all (or last as long). Instead, it seems to get weakened and mix with something else, producing a different smell.
As far as making a fragrance "skunky," I can imagine that might happen if the person is eating a lot of junk food, spicy food, food rich in garlic, etc.