What should a person allergic to sulfa based antibiotics be careful about? is there a comprehensive list of these antibiotics and is sulfur ok?

Sulfa is sulfa.: Sulfa antibiotics can cause severe reactions. These reactions can get started and continue to get worse even after the antibiotic is stopped; Stevens-Johnson syndrome is an example. Generally they are easily identified, having sulfa- as a prefix (such as sulfacetamide). Ask the pharmacist regarding oral antibiotics, but be careful with OTC ointments and eyedrops. Sulfur is not usually related.

Sulfa avoidance: Although cross-sensitivity to drugs with a similar sulfa structure was once suspected to be likely, this has not shown to be true. This only drug you need to avoid is sulfa (Bactrim, Septra (sulfamethoxazole and trimethoprim) etc). Read the label carefully. Note that it has nothing to do with sulfate or sulfite.