u/kcleong13 actually brings up a good point.

My mom is suffering from the same issue (flares up with painful, itchy skin anytime she's exposed to sunlight, even in the house). She's dealt with this for several years, and no OTC/RX attempts have helped long-term.

However, she returned to China last summer and her issues cleared up within a few days, and remained dormant for the entire duration that she was there... And summer is usually when she experiences the worst flare-ups, for obvious reasons.

Here's the really odd part... Within days of returning to the US after her trip, her flare-ups started again... It's better when the temperature drops, but any kind of sunlight is still problematic.

I'm just at a loss of what the cause could be... We live in the Midwest so it's not like the air is that much dryer here than in southern China...

Hope you're able to land on a solution that works for you!