Cobalt is a metal that is commonly found in soil and sea water, as well as in various industrial compounds. It is usually found in association with another metal, nickel.
Most alloys and salts contain both these metals, their separation being too costly to be feasible. Cobalt is usually used and known as cobalt(II) dichloride hexahydrate or cobalt blue.
Sources of Cobalt
- Cobalt blue is a pigment used to color glass, porcelain, ceramics, pottery, and enamels. It is found in green and blue watercolors and crayons as well.
- Cobalt is very often present in metal-plated buckles and buttons because it is used as an oxidizing agent in electroplating.
- It is used in metal alloys, such as that used to make drills, other cutting tools, and machine parts.
- Cobalt oxides are found in cement.
- It is also used in automobile exhaust controls as an oxidizing agent and in the manufacture of rubber tires.
- Cobalt naphthenate is used as a catalyst to produce polyester resins.
Allergic reactions to cobalt may include allergic contact dermatitis, though irritant dermatitis also occurs frequently.
Erythema multiforme rashes may occur, as well as contact dermatitis caused by contact with airborne cobalt particles.
In a few cases of cobalt allergy, the administration of vitamin B12 injections also causes redness, tenderness, and pruritus at the injection site.
A few others have reported the occurrence of chronic resistant hand eczema following the oral administration of vitamin B12. Some individuals present with asthmatic symptoms.
Cobalt allergy is often found to coexist with nickel allergy in many people. Thus, the objects that cause cobalt allergy are also found to contain nickel, which is itself a powerful sensitizing agent.
The symptoms of the so-called cobalt allergy may be due to nickel allergy as well.
Individuals of non-Caucasian origin are at a higher risk for cobalt allergy.
Diagnosis and Treatment
Cobalt allergy is usually diagnosed by studying the patient’s medical history followed by patch testing using 2% cobalt chloride in aqueous solution.
This should always include nickel testing as well, though pure nickel and cobalt solutions are very difficult to obtain.
These are not meant to elicit cross-reaction between the two metals, which is quite rare, but separate simultaneous sensitizations to both of them. Skin testing with 1:1000 cobalt chloride will yield a delayed tuberculin reaction in an individual without atopy.
Treatment consists of avoiding all contact with sources of cobalt. Treatment of allergic dermatitis includes local emollients, topical corticosteroids to suppress allergic reactions in the skin, and treatment of secondary infection, if any.
Complete avoidance of the offending metal, or, if this is impossible, the use of methods to prevent exposure is very important.
These include the use of plastic or wooden handles for metal instruments, vinyl or rubber gloves, coating the item with multiple layers of clear nail polish, and no-touch techniques wherever feasible.
Reviewed by Susha Cheriyedath, MSc
- Rietschel, R. L., & Fowler, J. F. (2001). Fisher's Contact Dermatitis (5th ed.). Lippincott Williams and Wilkins.
- Ruff, C. A., & Belsito, D. V. (2006). The impact of various patient factors on contact allergy to nickel, cobalt, and chromate. Journal of the American Academy of Dermatology, 55(1), 32-39. Retrieved from http://dx.doi.org/10.1016/j.jaad.2006.04.015.