Toxic epidermal necrolysis (TEN), also known as Lyell's syndrome and autoimmune cross-targeting

Autoimmune cross-targeting hypothesis suggests that simultaneous infections on one target triggers autoimmunity.  One infection on the outside of the target cell and one infection, like a virus, on the inside of the target.  

Lyell's syndrome is the acute onset of scalding skin triggered by a new medication
http://www.ncbi.nlm.nih.gov/pubmed/19766401

pemphigoid after lyell's syndrome
http://www.sciencedirect.com/science/article/pii/S0161642011008955

Main trigger is sulfa drugs. Sulfonamide antibiotics inhibit a bacteria's ability to make folic acid/dihydrofolic which are needed to make DNA.

People get their folic acid from their diet. (sulfa drug do not inhibit our DNA production)

Having said that it is not harmful for DNA production :

There could be a big difference between the organic MSM sulfur our body uses normally and the drug forms of sulfur.  Although our DNA production may not be an issue it could be that the drug forms of sulfur when "used by our cells" are actually viewed by our body's immune system as foreign.

Sulfa is used in our muscle and skin cells.

So in the autoimmune cross-targeting hypothesis this sulfa drug replaces the virus as foreign. It is unclear right now what infection would mark the outside.  It could be any skin infection: fungal, mycobacterial, staph, or mycoplasmas.