I know it is true that people self diagnose. That often happens as a result of confusing sulfates, sulfur, sulfa (sonfonamides), and sulfites. I looked it up to see how these compounds were metabolized and how they were related and I found this article. Hopefully this will help differentiate one from the other. Most importantly, being sensitive to one compound doesn't mean you are sensitive to all of them.
Sulfa Allergy
Antibiotics such as Co-Trimoxazole, sold under the brand name Septrin; Sulfamethoxazole, brand-name Gantanol; and Trimethoprim-Sulfamethoxazole, brand name Bactrim; are classed as sulfonamides. These drugs may be used to treat bacterial infections of the digestive or reproductive tracts. They're effective for many people, but some people develop an immune system response to sulfonamides that produces an allergic reaction. The sufonamide bonds to human protein, producing large molecules that can cause you to break out in hives, or swelling of the lips and other mucous membranes, or even difficulty breathing.
Sulfa vs. Sulfites
Sulfonamides are not the same as sulfites such as sulfur dioxide or sulfate salts. These chemical compounds are sometimes used to preserve foods. Your body metabolizes sulfites and sulfates differently than it does sulfa drugs. Being allergic to sulfa drugs doesn't predispose you to a sulfite allergy and vice-versa. Your body conversts the sulfa compounds used as food preservatives to sulfur dioxide. People with asthma are particularly susceptible to bronchospasms when they're exposed to these preservatives.
Sulfa and Food
Sulfonamides are used in medications, not foods. If you have a sulfa allergy, you don't have to avoid any particular foods. Though some people with sulfa allergies may also be sensitive to sulfites in food, the two allergies are not relates. Inform your doctor and your pharmacist if you've been previously diagnosed with a sulfa allergy. If you experience a reaction such as this after taking any antibiotic or other medication, contact your doctor immediately and seek emergency help.
http://www.livestrong.com/article/475626-foods-to-avoid-for-a-sulfa-allergy/#ixzz2Bk5xu4DF