Hi, Sorry for delayed response, just seen 2 years after your post. No sadly no luck figuring what issue is. I react badly to some chemicals ie Paints/varnishes but there is something in the Lexus rx 450h thats not in the 400h. Wish i could find out what it is as keen to stick with brand. Gone back to driving old 400h.

 

I would have guessed some chemical cleaner. My second guess would be a windshield with a warp. A rock took out the windshield on an old Vette years ago, the independent shop put in a windshield that drove me crazy, they finally agreed to replace it and the issue went away.

 

A lot of plastics and other materials in new cars these days are manufactured with different chemical composition to cars of yester years, mainly removal of petroleum based ingredients, as we gradually reduce our dependency on oil. Maybe the fumes from these newer materials could be causing the headaches, but I suspect the issue could be the fumes from commercial cleaners used to clean the interiors.

I suggest driving a brand new vehicle that has not yet been detailed like how a pre-loved vehicle would have been, and see if the symptoms re-occur.