Updated May 24, 2015.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

What is Contact Dermatitis?

Contact dermatitis is an itchy, blistering skin rash typically caused by the direct contact of a substance with the skin. There are 2 types of contact dermatitis: irritant and allergic. This difference is often difficult to tell apart, and is not usually an important distinction to make. Contact dermatitis results in 5.7 million doctor visits each year in the United States, and all ages are affected.

Females are slightly more commonly affected than males, and teenagers and middle-aged adults seems to be the most common age groups affected.

What is Vitamin B12?

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 multi-vitamins contain an adequate amount of vitamin B12 for good health.

Vitamin B12 Deficiency

The absorption of vitamin B12 is very complicated and 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, and people suffering from this condition may need to take oral or injectable vitamin B12 supplementation. Other people take large amounts of vitamin B12, particularly with other forms of vitamin B – termed vitamin B complex – for the purpose of “improved health”.

Since the cobalmin molecule contains a cobalt atom, taking large amounts of vitamin B12 (in either oral or injectable forms) may result in rashes and itching in people with a history of cobalt allergy.

While these reactions are not likely to be dangerous, they can result in an uncomfortable itchy rash. People with vitamin B12 deficiency and cobalt allergy should therefore only take as much vitamin B12 to maintain adequate levels as measured by blood tests.

How is Cobalt Allergy Diagnosed?

The diagnosis of cobalt allergy should be considered when a person who takes vitamin B12 supplements has any acute or chronic rash that itches. The rash classically has small blisters containing clear fluid, but can swell, crust, ooze or peel in other cases. The diagnosis is made with a patch test, which involves the placement of cobalt, and 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 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.

Watch how patch testing is performed.

How is Cobalt Allergy Treated?

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 on a blood test.

Sources:

Brescoll J, Daveluy S. A Review of Vitamin B12 in Dermatology. Am J Clin Dermatol. 2015;16:27-33.

Beltrani VS, Bernstein IL, Cohen DE, Fonacier L. Contact Dermatitis: A Practice Parameter. Ann Allergy Asthma Immunol. 2006;97:S1-38.

DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.