Key Takeaways
People who are allergic to cobalt might also be allergic to vitamin B12. A cobalt allergy can cause a red, itchy rash called contact dermatitis.Most cobalt exposure is from makeup or industrial uses like batteries, along with B12 supplements.
Allergic reactions to vitamin B12 are often linked to a rare cobalt allergy, leading to symptoms like contact dermatitis. Immediate medical help is vital if side effects such as anaphylaxis occur, though these cases are uncommon.
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When to Seek Emergency Care
In rare instances, vitamin B12 injections can cause life-threatening anaphylaxis, which is always a medical emergency. Anaphylaxis symptoms include:
Itching
Hives
Shortness of breath
Swollen throat or trouble swallowing
Wheezing
Vomiting
Diarrhea
Seek immediate medical help if you experience these symptoms.
Spotting the Signs of a Vitamin B12 Allergy
Taking large amounts of vitamin B12 can cause contact dermatitis if you are sensitive to cobalt. While contact dermatitis is usually not life-threatening, a vitamin B12 allergy can rarely lead to severe reactions.
There are two types of contact dermatitis: irritant and allergic. Irritants can cause irritant contact dermatitis in anyone, whereas allergic contact dermatitis is only possible if you’re allergic to the substance.
A contact dermatitis rash may appear:
Red, itchy, burning, and/or stingingSometimes blistering or oozingDue to direct contact with the irritant
Your skin could become dry, cracked, inflamed, and tender. This reaction can occur anywhere on your body.
Who Is at Risk for Contact Dermatitis?
Contact dermatitis results in millions of doctor visits each year in the United States. It affects people of all ages, with research suggesting that about 20% of people experience this condition.
Females are slightly more affected than males. Teenagers and middle-aged adults tend to have it more often than other age groups.
Cobalt and Causes of a B12 Allergy
The allergy can be triggered by taking vitamin B12 supplements because B12 contains cobalt atoms.
Vitamin B12 supplements (either oral or injectable) are normally taken to support a healthy nervous system and are often needed in people who are deficient in vitamin B12. The deficiency can occur when people have difficulty absorbing foods with B12 in the small intestine.
Cobalt allergies often develop in people exposed to it through eye makeup, tattoos, or industrial products, leading to an itchy, red, scaly rash. Once sensitized, you’ll experience allergic contact dermatitis whenever exposed to cobalt.
B12 deficiency can be challenging to manage if you have a cobalt allergy. Discuss with your healthcare provider how much B12 is safe for you.
Testing for Vitamin B12 Sensitivity
A cobalt allergy is diagnosed with a patch test. This test places a small cobalt-laden patch on your back for about 48 hours.
After 48 hours, your reaction is evaluated and then checked again a day or two later. A positive result shows blisters, redness, and/or mild swelling.
Vitamin B12 sensitivity may show up as a rash after you take a supplement. In rare cases, a severe allergic reaction called anaphylaxis can occur if you take large amounts of vitamin B12 orally or via injection.
How to Manage a Vitamin B12 Allergy
You can treat a rash from allergic contact dermatitis with topical or systemic corticosteroids. However, the best way to manage a cobalt allergy is to avoid high doses of vitamin B12 and products containing cobalt.
For B12 deficiency, only take the minimum amount needed to get your levels to normal.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Wajih Ullah M, Amray A, Qaseem A, et al. Anaphylactic Reaction to Cyanocobalamin: A Case Report. Cureus. 2018 May 5;10(5):e2582. doi: 10.7759/cureus.2582
American Academy of Allergy and Asthma and Immunology. Anaphylaxis.
Ullah MW, Amray A, Qaseem A, Siddiqui T, Naeem T. Anaphylactic reaction to cyanocobalamin: A case report. 2018;10(5):e2582. Published 2018 May 5. doi:10.7759/cureus.2582
American Academy of Dermatology Association. Eczema types: contact dermatitis signs and symptoms.
Adler BL, DeLeo VA. Allergic contact dermatitis. JAMA Dermatol. 2021;157(3):364. doi: 10.1001/jamadermatol.2020.5639
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National Institutes of Health Office of Dietary Supplements. Vitamin B12.
Lidén C, Andersson N, Julander A, Matura M. Cobalt allergy: suitable test concentration, and concomitant reactivity to nickel and chromium. Contact Derm. 2016;74(6):360-7. doi:10.1111/cod.12568
Additional Reading
American Academy of Allergy, Asthma and Immunology; American College of Allergy, Asthma and Immunology. Contact dermatitis: a practice parameter [published correction appears in Ann Allergy Asthma Immunol. 2006 Dec;97(6):819. Beltrani, Vincent S [removed]; Bernstein, I Leonard [removed]; Cohen, David E [removed]; Fonacier, Luz [removed]]. Ann Allergy Asthma Immunol. 2006;97(3 Suppl 2):S1-S38.
Daniel More, MD, is a board-certified allergist, clinical immunologist, and assistant clinical professor at the University of California, San Francisco School of Medicine.
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