I developed Burning Mouth Syndrome 3 weeks ago. I never heard of this until I did a search, it describes what I have. There appears to be several underlying causes and the one that fits my situation is vitamin deficiencies. My B12 level was/is down at 217, my folate was not tested. The BMS started the day after I started sub lingual mB12 and Metafolin, I'm not sure whether it was just a coincidence. I've discontinued Metafolin and started Thorne B Complex. The burning chemical symptoms that I have are still there so I'm guessing it's not the Metafolin. Has anyone had this? My thinking is that I may not need folate because my levels are normal and that I need to increase my B12 status which is what I'm doing. I'm stopping the B Complex for now to see if it goes away.