Way too many scent-related things cause headaches for me to speculate, but in my personal case other people's cheap perfume/body lotion/room spray will give me headaches and sometimes set off my allergies, but bpal generally doesn't. (full disclaimer: this also applies to higher quality perfumes of all sorts and more naturally scented products like lush) Skin chemistry and things like that play a big part in the wearing bpal experience because it's an oil-based perfume and not an alcohol-based one, and so will smell different and have different strengths on different people's skin (and even wear differently on your own skin depending on season/hormones/etc).

Anyway, i won't go all bpalvangelist on you, but if there's anything in particular you're interested in, i'd be happy to natter on and on at length about it.