I experienced a sudden flare-up a few months ago. I normally have pain in my legs and feet, weakness, balance issue, etc. but his was a body wide burning feeling, like a really bad sunburn. My clothes were unbearably painful, sitting, everything burned. I first suspected my meds, so we changed a few things with no effect. A few weeks into his I developed the biggest, ugliest cold sore I ever had, and it took weeks to heal. It wasn't as painful as I remember them being, but gabapentin is very effective for post-herpetic neuralgia, so dampened the pain.
It now seems likely that a shingles type virus was responsible for the burning. Once the blister broke out the symptoms gradually lessened, and I am back to my normal level of skin sensitivity, which is still elevated, but tolerable.
My doctor has given me a prescription for an acyclovir type medication to take immediately if the symptoms return, or I develop another cold sore. If a virus can cause a flare, I would guess an infection could as well.

Absolutely. Viruses, infections, bacteria, inflammation, and any kind of stress... Just about anything that can alter body chemistry can cause pain flares of all kinds.

Susanne, have you ever tried an antihistamine for those body-wide burning flares? Epsom salts or baking soda bath?

Doc

Yes, Mrs. D suggested Benadryl. It helped me sleep when the burning was at it's worst, which was a big help.