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Allergy to cobalt

Authors: Vanessa Ngan, Staff Writer, 2002; Updated: Elena Redl, Medical Student, Medical University of Vienna, Austria; Dr Martin Keefe, Dermatologist, New Zealand, May 2021; further minor update 2023.


What is cobalt allergy?

Cobalt is one of the most common metals to cause contact allergy via a delayed hypersensitivity reaction. It is also called cobalt dichloride hexahydrate, cobalt blue, cobaltous chloride hexahydrate, and cobalt hexahydrate. The name comes from the German word ‘Kobold’ meaning goblin or elf.

Cobalt was the American Contact Dermatitis Society’s 2016 Contact Allergen of the Year.

Who gets cobalt allergy?

Cobalt allergy affects about 2% of the general population and can develop at any age, including in children. It shows a female predominance (2:1) and is commonly associated with atopic dermatitis.

One study reported an increased prevalence of cobalt allergy in people with skin of colour.

Cobalt allergy can coexist with other metal allergies such as nickel and chromate.

What causes cobalt allergy?

Cobalt is commonly used as a binding agent in the manufacture of ‘hard’ metals with increased wear resistance such as drills and cutting tools.

It is also found in:

Cobalt nanoparticles may cause reactions in sensitised individuals and may be an important source of occupational exposure.

What are the clinical features of cobalt allergy?

  • Cobalt allergy usually presents as a chronic or subacute allergic contact dermatitis at sites with direct contact but may become more extensive
  • Photosensitive dermatitis has been reported with cement and pig fodder [see Photosensitivity]
  • Cobalt blue used in light blue tattoos can cause sarcoidal allergic reactions
  • Erythema multiforme has been rarely reported
  • Dust containing cobalt may cause asthma in metal workers.

What are the complications of cobalt allergy?

  • Secondary bacterial infection or autoeczematisation of the dermatitis.
  • Patients with allergic contact dermatitis to cobalt taking oral vitamin B12 (cobalamin) supplements may develop chronic vesicular hand dermatitis, cheilitis, stomatitis, or systemic contact dermatitis. Vitamin B12 injections (cyanocobalamin) can also cause local injection site reactions, hand dermatitis, and anaphylaxis.
  • Orthopaedic and other implanted metal devices can sometimes result in intractable generalised dermatitis in cobalt-allergic patients. Pain and loosening of the implant have been reported.

How is cobalt allergy diagnosed?

Allergic contact dermatitis due to cobalt is diagnosed on patch testing with 1% cobalt chloride hexahydrate. A positive reaction to nickel is likely to be due to dual sensitisation rather than cross-reactivity.

Cobalt naphthenate used in the polyester resin and plastics manufacturing industries can also cause an allergic contact dermatitis, but this may not be detected by the standard patch test with cobalt chloride.

Photopatch testing with cobalt is required if a photocontact dermatitis is suspected [see Phototesting].

Purpuric patch test reactions are peculiar to cobalt due to a poral reaction to cobalt accumulation in the eccrine glands and are not indicative of cobalt allergy.

Rarely, intradermal tests or oral challenge tests may be appropriate.

Positive patch test to cobalt

What is the differential diagnosis for cobalt allergy?

What is the treatment for cobalt allergy?

Cobalt allergy is treated by identifying and avoiding the source of exposure.

Identify potential sources of exposure at work using material safety data sheets. Read product labels. The presence of cobalt in a metal object can be confirmed using a commercial 2-nitroso-1-naphthol-4-sulfonic acid spot-test. A clue to cobalt-containing jewellery is a dark silver rather than shiny appearance.

To minimise cobalt exposure:

  • Use metal instruments such as scissors, kitchen utensils, and combs that have plastic or wooden handle grips
  • Wear vinyl or rubber gloves to avoid contact
  • Items such as keys can be coated with several layers of clear nail polish
  • In the workplace wear personal protective equipment and employ no-touch techniques
  • Alert your doctor and dentist.

Contact dermatitis treatment includes:

What is the outcome for cobalt allergy?

Allergic contact dermatitis due to cobalt will settle if contact with cobalt can be avoided.

Further information

CAS number: 7791-13-1

Appearance: Silvery grey, shiny, hard metal

Sensitiser: cobalt

Patch test:

  • 1% cobalt chloride in aqueous solution
  • 1% cobalt sulphate in aqueous solution
  • 5% cobalt naphthenate in aqueous solution



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  • Fowler JF Jr. Cobalt. Dermatitis. 2016;27(1):3–8. doi:10.1097/DER.0000000000000154. Journal
  • Midander K, Werner P, Isaksson M, et al. Cobalt nanoparticles cause allergic contact dermatitis in humans. Br J Dermatol. 2023;188(2):278-287. doi:10.1093/bjd/ljac043 Journal
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  • Thyssen JP, Menné T, Johansen JD, et al. A spot test for detection of cobalt release — early experience and findings. Contact Dermatitis. 2010;63(2):63–9. doi:10.1111/j.1600-0536.2010.01749.x. Journal

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