Vitamin B-12 comes from animal by-products, eggs and milk and may cause adverse reactions if you have an allergy to one or more of these foods. Reactions to vitamin B-12 can cause complications in your skin, gastrointestinal system and respiratory system. You need to report any symptoms that develop from taking a vitamin B-12 supplement to your health care provider immediately. A severe allergic reaction can cause life-threatening symptoms that may result in death if not treated properly.
Skin Reactions
Skin outbreaks are common with most supplement and allergy reactions. The most common reaction caused by taking a new supplement is hives. Hives cause inflammation of the skin that develops in clusters of welts, according to the American Academy of Allergy, Asthma and Immunology. The welts may develop in various shapes and sizes and are extremely itchy. Hives typically clear within a few hours and are harmless unless they develop in your throat or inner ear. You may also develop general tingling, itching and redness within a few minutes of taking vitamin B-12.
Gastrointestinal Reactions
Some gastrointestinal reactions from vitamin B-12 supplements may not be from an allergic reaction, but caused by minor irritation to the lining of your stomach. Try eating food before taking the supplement to see if that improves your digestive symptoms. An allergic reaction will cause inflammation to develop in your digestive system, bringing bloating, gas, diarrhea, stomach pain, cramping, vomiting and nausea. If you notice blood in your vomit or stool, call your doctor immediately.
Allergic Asthma
Allergic asthma, caused by inflammation in your airways and lungs, occurs within minutes of taking a vitamin B-12 supplement. Common symptoms include difficulty breathing, coughing, shortness of breath, lightheadedness and wheezing. Wheezing is a high-pitched sound made by the small opening in the throat when it's swollen. Asthma is a common sign of anaphylaxis, a severe allergic reaction. If you're unable to breathe, call 911 immediately.
Allergic Rhinitis
Allergic rhinitis is the inflammation of your nasal passages due to increased levels of histamine in the body. Histamine results during an allergic reaction to protect the body, but instead of protecting the body, it causes inflammation in soft tissues. This results in nasal congestion, sneezing, a runny nose, post-nasal drip, sinus headaches, facial tenderness and nasal pressure. Report any severe head pain to your doctor because it may be a sign of a more serious condition.
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