Allergy to Vitamin B12

Allergic Contact Dermatitis to Cobalt and Vitamin B12 Allergy

An allergy to cobalt can be triggered by taking vitamin B12 (cobalamin) since the cobalamin molecule contains a cobalt atom. Taking large amounts of vitamin B12 (in either oral or injectable forms) may result in contact dermatitis, producing rashes and itching in people with a history of cobalt allergy.

Woman itching her arm.
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There have been some case reports of patients developing these reactions in association with vitamin B12 supplementation. Contact dermatitis is a rash that is not usually life-threatening. The rare condition of vitamin B12 allergy can be life-threatening, although there are few reports of it in the medical literature.


Contact dermatitis is a red, sometimes blistering skin rash typically caused by the direct contact of a substance with the skin. There are two types of contact dermatitis: irritant and allergic.

While irritants will cause irritant dermatitis for most people who are exposed to sufficient amounts of the offending chemical, allergens will only cause allergic contact dermatitis in people who are sensitized (that is, allergic) to those substances.

Contact dermatitis results in millions of doctor visits each year in the United States, and all ages are affected. Research suggests that 20% of all people are affected by this condition. Females are slightly more commonly affected than males, and teenagers and middle-aged adults seem to be the most common age groups affected.

Rarely, intramuscular injections of vitamin B12 have also been associated with life-threatening anaphylaxis. The symptoms of anaphylaxis may include itching, hives, shortness of breath, wheezing, vomiting, diarrhea, or anaphylactic shock.


Vitamin B12, also called cobalamin, is a water-soluble vitamin that plays an important role in the formation of blood cells and in the normal function of the nervous symptom. Cobalamin is usually available from dietary sources, and most multivitamins contain an amount of vitamin B12 adequate for good health.

Vitamin B12 Deficiency

The absorption of vitamin B12 is very complicated: it includes various steps that are prone to defects, which could lead to poor absorption of vitamin B12 from the small intestine. As a result, vitamin B12 deficiency is relatively common.

People suffering from this condition may need oral or injectable vitamin B12 supplements. Other people take large amounts of vitamin B12, particularly with other forms of vitamin B—termed vitamin B complex—hoping to gain “improved health.”

Cobalt and Vitamin B12 Allergy

Cobalt allergy typically presents when a person who is exposed to cobalt in cosmetics (eye makeup, in particular), in tattoos, or in industrial products develops an itchy, red, scaly rash that can sometimes even blister.

If a patient becomes sensitized to cobalt, they will develop a rash (allergic contact dermatitis) after re-exposure (i.e., skin contact) to cobalt. While these reactions are not likely to be dangerous, they can result in an uncomfortable itchy rash. However, this is not the way most cases of cobalt contact allergy present.

People with vitamin B12 deficiency and cobalt allergy should therefore only take as much vitamin B12 as is needed to maintain adequate levels.


Cobalt allergy diagnosis is made with a patch test, which involves the placement of cobalt, along with other chemicals, on the back for approximately 48 hours (it is not the same as allergy skin prick testing). This typically is done with a paper tape system, such as the TRUE test.

The TRUE test is the only FDA-approved test for contact dermatitis in the United States, although some allergists and dermatologists will develop more extensive patch test panels with chemicals purchased from Canada or Europe.

The results of the test are interpreted at 48 hours after placement, and again at 72 or 96 hours after placement.

A positive test is confirmed when there are blisters, redness, and/or mild swelling at the site of the particular chemical in question. The site of the positive test usually itches, although the reaction size is typically limited to the site of contact and therefore is usually smaller than a dime.


The rash associated with cobalt allergy contact dermatitis can be treated with topical corticosteroids or systemic corticosteroids (oral versus injectable). However, cobalt allergy is best treated with avoidance of large doses of vitamin B12.

People with vitamin B12 deficiency should only take the minimum amount of vitamin B12 that it takes to maintain normal levels of vitamin B12, as measured by a blood test.

Frequently Asked Questions

  • Can you be allergic to vitamin B12?

    Yes, people who are allergic to cobalt will have an allergic reaction to vitamin B12, also known as cobalamin. Cobalamin contains cobalt atoms. B12 allergies, however, are rare.

  • Can too much vitamin B12 cause a rash or itchy skin?

    Yes, taking large amounts of vitamin 12 can cause a skin reaction in people who are sensitive to cobalt. The symptoms include an itchy rash. 

  • How do you know if you are allergic to B12 or cobalt?

    A cobalt allergy typically first occurs after being exposed to cobalt in eye makeup, tattoos, or industrial products. It appears as an itchy, red, scaly rash. Once someone is sensitized to cobalt, reactions can occur with re-exposure to smaller amounts of cobalt. 

    A vitamin B12 sensitivity can appear as a rash after taking supplements. A severe allergic reaction, known as anaphylaxis, can occur after taking large amounts of vitamin B12 orally or as an injection. 

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Article Sources
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Additional Reading
  • Beltrani VS, Bernstein IL, Cohen DE, Fonacier L. Contact Dermatitis: A Practice Parameter. Ann Allergy Asthma Immunol. 2006;97:S1-38.
  • Brescoll J, Daveluy S. A Review of Vitamin B12 in Dermatology. Am J Clin Dermatol. 2015;16:27-33.