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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.
Introduction
Demographics
Causes
Clinical features
Complications
Diagnosis
Differential diagnoses
Treatment
Outcome
Further information
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.
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.
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.
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.
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:
Contact dermatitis treatment includes:
Allergic contact dermatitis due to cobalt will settle if contact with cobalt can be avoided.
CAS number: 7791-13-1
Appearance: Silvery grey, shiny, hard metal
Sensitiser: cobalt
Patch test: