I went to our immediate supervisor. I was a teacher, so I also coordinated info with the school nurse. I explained that this was a medical condition for me, not a "pet peeve." When asked, I took in document ation from my doctors (allergist, and neurologist too, b/c strong fragrances give me migraines). I was polite about it, and my supervisor (principal) dealt with the co-worker. I had to do this multiple times, but most of my colleagues were understanding. When someone was not, I was apologetic with them... but explained that, just like needing accomodations for things like wheelchairs, I needed accomodations for my health issue.

My own passing out or just wheezing and choking every time I got near someone living in a toxic cloud tends to get the point across. But for those less grossly affected, I would just ask them politely to not wear perfume because it is causing you problems (if it does).