We are not aware of any side effects of Calagel. However, if you are allergic to sulfites, you could experience: a reaction that can vary from mild to life threatening. The most common symptoms are mild and involve a skin rash accompanied by redness, hives, itching, flushing, tingling, and swelling. Respiratory symptoms include difficulty breathing, wheezing, and stridor. Gastrointestinal reactions involve nausea and stomach cramps. Less common but more serious signs include low blood pressure, shock, extreme difficulty breathing, and loss of consciousness. DO NOT USE Calagel IF ALLERGIC TO SULFITES.