Sulfites are a common presence in daily life that most people are likely unaware of. It is in almost every wine and fermented beverage, used frequently as a food preservative, and also as a preservative in medications. For many people, this doesn't present much of a problem, but there are those who have an allergy, and those with asthma have been shown to be affected by sulfites. Along with these problems, there are people who demonstrate a sensitivity to the sulfites, particularly in relation to headaches, though most of the information on sulfites causing headaches is anecdotal rather than scientific. As common as sulfites have become, knowing what to avoid can be very important for a healthy life.
The only thing that is required by the FDA to have a label detailing the sulfite content is wine. Almost all wines contain sulfites, as it is a natural by-product of yeast during fermentation. White wines have a slightly higher level of sulfites than red wines, but generally speaking there will be around 80 mg/liter in a glass of wine. To avoid sulfites in wines, look for those labeled organic. In the United States, an organic wine is required to be made without sulfites, but they are rare as the lack of sulfites causes them to be extremely perishable and often a strange smell accompanies them due to the aldehydes. When shopping outside of the United States, there are few regulations on the level of sulfites being reported, so be aware that it is a reasonably sure bet that all wines have some amount of sulfite.
Though the FDA does not require foods to be labeled with sulfite levels unless it has been added (not if it is simply contained in another ingredient), many companies voluntarily will put this information on their nutritional labels. To avoid sulfites in food, try to stay away from foods with a lot of preservatives such as dried fruits, lemon and lime juice, and pickled onions. Dried vegetables, wine vinegar, and preserved fruits other than dried also contain high levels of sulfites. For the best avoidance of sulfites, shopping for organic foods is a great idea.
One final word of caution on hidden sulfites, medications often contain sulfites. Not only do sulfites prevent browning, but there are also antioxidant quality which is taken advantage of by adding this ingredient. One common medication you will find sulfites in is injectable epinephrine. Most asthma medications have had sulfites removed, as asthmatics have been known to react even to the vapors that come from fermented beverages. As with any medication, talk to a doctor about the medication being prescribed if there is concern about the sulfite level in a prescription.