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  Atopic eczema, irritant dermatitis and contact dermatitis


Irritants that cause contact dermatitis are called contact allergens. These allergens are identified by the diagnostic procedure of patch testing in dermatitis patients. The North American Contact Dermatitis Group (NACDG) recognizes ten major contact allergens. They can be further categorized according to their form and usage.


  • Nickel (nickel sulfate)
  • Gold (sodium gold thiosulfate)
  • Cobalt (cobalt chloride)


  • Formaldehyde
  • Quaternium-15
  • Thimerosal


  • Neomycin sulfate
  • Bacitracin 13


  • Fragrance mix
  • Balsam of Peru (Myroxylon pereirae)


Nickel is a solid silver-colored metal that can be a constituent of jewelry, buckles, snaps, and other substances made of metal. NACDG tests report nickel as the most common allergen, with 14% of patch test patients showing positive reaction to it. Global figures also show nickel to be the most common allergen with some patch test centers reporting 30-40% positive results in all cases. However, nickel reactions have a projected 50% significance to an existing dermatitis condition.

Ear piercing has a major role to play in the high incidence of nickel reactions, since the metal posts used in the process discharge nickel and facilitate direct contact with the sensitive skin. Due to its high presence in jewelry, nickel allergy is more common in women.

Its clinical occurrences are:

  • Earring dermatitis
  • Necklace or watch dermatitis due to a nickel-based metal back/band
  • Belt buckle or snap dermatitis in the mid-abdomen
  • Eyelid dermatitis from metal eyelash curlers

Concurrent nickel and cobalt allergy is also reported from substances that combine the two metals. Sweating aggravates the condition as it increases the metal production of the substance. The dimethylglyoxime test is ideal for determining whether a substance contains nickel. Those prone to nickel reactions should switch to jewelry made of stainless steel or gold.


There are two forms of gold allergy:

1. Systemic reactions: Seen in persons in whom gold is used as a therapy for conditions like rheumatoid arthritis, pemphigus, and lupus erythematosus.
2. Topical gold (auranofin) triggers allergic contact dermatitis

Gold is an inert metal that is used in jewelry, dentistry and also the electronics sector. The ideal potency of a patch test contains gold sodium thiosulfate 0.5%., though this allergen is not available in the TRUE® Test. There is a wide discrepancy in the global extent of gold reactions, regular testing generally shows a range from 0.78% to 10%. In the NACDG tests, 90% of gold allergy was found in women.

The clinical occurrences of dermatitis are:

  • Hand
  • Facial
  • Eyelid


Cobalt is a hard metal that commonly occurs in combination with other metals such as nickel, chromium, molybdenum, and tungsten, to increase hardness and durability. Hence, an estimated 80% of patients reporting cobalt allergy also react to chromate (more in men) or nickel (more in women).

The exposure vehicles of cobalt are jewelry, snaps, buttons, tools, cosmetics, hair dyes, joint replacements, ceramics, enamel, cement, paints, and resins.


Formaldehyde is a colorless liquid or gas that is universally found in almost all workplaces and circulates in the air from cigarette smoke and automobile emissions. It is the most common ingredient in cosmetics, medications, textiles, paints and paper. Now-a-days, it is avoided in personal care products and cosmetics. However, formaldehyde reaction occurs due to the use of other formaldehyde- discharging preservatives.

Formaldehyde resins, which are used in 'wash-and-wear' or wrinkle-free garments, are also a major cause textile dermatitis. These resins are also released from plastic containers into products they contain.

The common occurrences of formaldehyde allergy are:

  • Irritant contact dermatitis
  • Allergic contact dermatitis
  • Contact urticaria
  • Mucous membrane irritation mostly in the conjunctiva and respiratory tract

Since formaldehyde is omnipresent, it is difficult to detect and avoid. Patch tests can often be unmanageable and must be checked for clinical relevance.


The preservative Quatermum-15 is a quaternium compound, which acts as a useful biocide against bacteria and fungi primarily Pseuclomonas aeruginosa and P. cepacia. Though it is used in many industries, occurrence of work-related contact dermatitis is not frequent. Its main vehicles are personal care preparations such as shampoos, moisturizers, conditioners, and soaps, body washes. It is also the most prevalent cosmetic preservative-based trigger of allergic contact dermatitis. Its reactivity could be linked to its production of formaldehyde.

80% of Quatermum-15 sensitive patients also show concurrent allergy with the latter and other formaldehyde releasing preservatives. Quaternium-15 exposure can be guarded against through educated reading of product label information.


Thimerosal - sodium ethylmercurithiosalicylate is a common preservative coming from the following sources:
  • Vaccines
  • Contact lens solution
  • Otic and ophthalmic solutions
  • Solutions for intradermal examinations
  • Antiseptics
  • Cosmetics

Patch testing shows mixed results with some positive and clinically relevant reactions, while others lacking the latter. Hence, regular testing should be the strategy, though NACDG has discontinued thimerosal testing since 2003.

Neomycin Sulfate

Neomycin is an antibiotic is a most common topical antibiotic and found in:

  • Antibacterial ointments
  • Hemorrhoid creams
  • Otic and ophthalmic products

It is often used in combination with other antibacterial agents (bacitracin, polymyxin, corticosteroids), hence reaction to it is presumably correlated.


Bacitracin is a topical antibiotic found in antibacterial and ophthalmic products, generally in combination with other topical antibiotics (mostly neomycin) and corticosteroids. It often shows concurrent sensitivity with neomycin. Clinical appearances are:

  • Allergic contact dermatitis
  • Anaphylaxis and contact urticaria (rarely)

Balsam of Peru

Balsam of Peru (Myroxylon pereirae) is an organically found fragrance that other than fragrance allergy manifests itself in reaction to spices (cloves, Jamaican pepper, cinnamon) colas, tobacco, wines and vermouth.

The NACDG identifies it as the third most prevalent allergen and The International Fragrance Association recommends its avoidance as a fragrance ingredient. Balsam of Peru was the major fragrance allergy before the development of the fragrance mix in 1970, which can also be the cause of allergy.

Fragrance Mix

NACDG marks fragrance mix as the fourth most common allergen (11.7%) and the commonest cosmetic trigger of allergic contact dermatitis.

Fragrance mix was introduced in 1970s and was a milestone in the recognition of a fragrance reaction. The existing mix is made of eight fragrances (1% each):

  • cinnamic alcohol
  • cinnamic aldehyde
  • eugenol
  • oak moss absolute
  • a-amyl cinnamic aldehyde
  • geraniol
  • hydroxycitronellal
  • isoeugenol

This basic mix identifies 70-80% of fragrance allergies.

Other than their use as pleasant aroma, these mixes also occur in the following forms:

  • In preparations (labeled unscented) that cover bad odors, known as masking fragrance. Patients who react to them should look for ‘fragrance free’ labels.
  • As a preservative or emollient