I am not sure why doctors don't tell their patients, but using a sunscreen with zinc oxide 5% or higher keeps the brown spots from recurring as fast. Of course they will come back and that's why you need to go in every 12-18 months for a "touch-up." I had to ASK my doctor about this or else I'm not sure she would've told me. I've used it everyday and my age spots have not come back or the ones that have are very pale.
I am going for my 1st touch up at the end of this summer and it's been 16 months since my last photofacial.
Walmart, Kroger, and Walgreens all sell this type of suncreen under their own brand. Neutrogena also sells it - I believe it's the Baby Pure and Free with pink/black/white bottle. Those are all $10 or less. Skinceuticals sells it for about $30. I've used both the expensive and the cheap. They all work.
Good Luck everyone!