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Patch Testing for contact dermatitis reactions to metals, chemicals, cosmetics

Contact allergen testing is an objective scientific method available to physicians to augment the diagnostic process. Often the contact allergen test response is the crucial piece of information that allows for the early identification of the offending allergen(s) and confirmation of a diagnosis of allergic contact dermatitis. Upon determining where exposure to the reacting allergen occurs, the patient can then take appropriate action to avoid exposure to the allergen and, if possible, to substitute non-allergenic agents.

Interpretation of reaction sites is based on the method recommended by the International Contact Dermatitis Research Group (ICDRG). It is important to note that skin tone affects the appearance of test results. Interpretation Key based on recommendations by the ICDRG.

Doubtful reaction
Faint macular or homogeneous erythema, no infiltration= ?
Extreme positivereaction
Coalescing vesicles/bullous reaction= +++
Weak positive reaction
Erythema Infiltration Discrete papules= +
Irritant reaction of different types*= IR
Strong positive reaction
Erythema Infiltration Papules Discrete vesicles= ++
Negative reaction= Not Tested

*Discrete patchy erythema or homogeneous erythema without infiltration, patchy follicular erythema. Petechiae and follicular pustules are usually irritant and do not normally indicate allergy. It is sometimes very difficult to distinguish between an irritant reaction and a very weak positive reaction. Retesting may be necessary to certify contact allergy. Patients who show a negative reaction to the allergens may be sensitive to substances other than those tested. Testing with complementary substances may be indicated.

True Positives

The majority of extreme positive reactions (+++) and strong positive reactions (++) reflect true positives. With weak positive reactions (+), there is a greater possibility that the reaction will not reflect a true-positive result.

For any true-positive reaction, the patient should be advised to avoid future allergen exposure. The relevance of true-positive reactions to current eruption and/or past allergen exposure must be confirmed with respect to
– the nature and distribution of the skin eruption;
– the validity of the relationship between allergen and recent exposure; and
– patient history, especially of allergic reactions.

Reactions that cannot be explained may be due to
– incomplete history;
– exposure to unsuspected, undetected, or unrecognized allergens;
– the ubiquitous nature of some allergens;
– cross-reactivity; or
– low environmental exposure to an allergen prior to testing.

With reactions of past or current relevance, detailed advice on avoiding the discovered allergen should be given to the patient.

Patch testing (Panel 1)
1. Nickel sulphate

Concentration:0.20 mg/cm²
Allergen component per patch:Nickel, 0.036 mg
Vehicle:Hydroxypropyl cellulose
Other substances to which the patient may react:Cobalt, chromium, disulfiram
Found in:Jewelry, metal, and metal-plated objects; occasionally in eye cosmetics

2. Wool alcohols (lanolin)

Concentration:1.00 mg/cm²
Allergen component per patch:Cholesterol, lanosterol, agnosterol (and dihydro derivatives); straight- and branched-chain aliphatic alcohols; 0.81 mg total (the active allergenic component has not been identified)
Synonyms and/or components:Lanolin, anhydrous lanolin, wool fat, wool wax, wool grease, ClearlinTM, GlossylanTM, Golden Dawn®, HycholTM, NodorianTM, SparklelanTM, adeps lanae anhydrous, aloholes lanae
Also modified lanolins, such as lanolin aid, lanolin alcohol, lanolin oil, lanolin wax, Amerchol L-101®, and Amerchol® CAB
Other substances to which the patient may react:Eucerin®, Aquaphor®
Found in:Cosmetics, soaps, and topical medications


3. Neomycin sulphate

Concentration:0.023 mg/cm²
Allergen component per patch:Neomycin sulfate, USP, 0.19 mg
Synonyms and/or components:Gentamicin sulfate, bacitracin, kanamycin, streptomycin sulfate injection, spectinomycin HCl, tobramycin sulfate
Found in:Topical antibiotics


4. Potassium dichromate

Concentration:0.023 mg/cm²
Allergen component per patch:Chromium, 0.0067 mg
Vehicle:Hydroxypropyl cellulose
Synonyms and/or components:Chromium, chrome, chromate, chromite
Found in:Cement, chrome-tanned leather, welding fumes, cutting oils, antirust paints, other industrial chemicals


5. Caine mix

Concentration:0.63 mg/cm²
Allergen component per patch:Benzocaine, USP, 0.364 mg; tetracaine HCl, USP, 0.063 mg; dibucaine HCl, USP, 0.064 mg
Synonyms and/or components:Benzocaine:ethyl aminobenzoate, p-aminobenzoic, acid (PABA) ethyl ester, Aethoform™, Americaine®, Anesthesin™, Anesthane™, Orthesin™, Parathesin™, Anesthone™Tetracaine HCl: tetracaine, Pontocaine®Dibucaine HCl: dibucaine, Nupercaine™
Other substances to which the patient may react:Benzoic acid derivatives:
PABA esters: procaine, benoxinate HCl, butamben picrate, butacaine, butethamine HCl, naepaine, orthocaine, propoxycaine, risocaine, chloroprocaine HClm-Aminobenzoic acid esters: metabutethamine, proparacaineBenzoic acid esters: cocaine HCl, amylocaine, benzamine, cyclomethycaine, meprylcaine HCl, metabutozycaine, piperocaine HCl, hexylcaine HCl, proparacaine HalOther agents: Procainamide, hydrochlorothiazide, PABA and PABA ester sunscreens, Azo® and aniline dyes, p-phenylenediamine, sulfonamides, sulfonylureas, p-aminosalicylic acid
Found in:Topical anesthetics


6. Fragrance mix

Concentration:0.43 mg/cm²
Allergen component per patch:Geraniol, 0.070 mg; cinnamaldehyde, 0.034 mg; hydroxycitronellal, 0.054 mg; cinnamyl alcohol, 0.054 mg; eugenol, 0.034 mg; isoeugenol, 0.015 mg; amylcinnamaldehyde, 0.015 mg; oak moss, 0.070 mg
Vehicle:Hydroxypropyl cellulose, cyclodextrin
Synonyms and/or components:Synonyms:cologne, toilet water, perfume, masking or unscented perfume or fragrance, aroma chemicals, essential oils of plants and animals.Individual fragrance allergens:cinnamic alcohol, cinnamic aldehyde, oak moss absolute, amylcinnamic alcohol, anisyl alcohol, benzyl alcohol, benzyl salicylate, coumarin, sandalwood oil, musk ambrette, wood tars
Other substances to which the patient may react:Balsam of Peru, ethylene bassylate (Musk T™), cloves, cinnamon, cassia oil, citronella candles
Found in:Fragrances, toiletries, scented household products, flavorings, food, industrial products


7. Colophony

Concentration:0.85 mg/cm²
Allergen component per patch:Colophony, 0.69 mg
Synonyms and/or components:Rosin, resina terebinthinae, gum rosin, rosin gum, W-W wood rosin, tall oil, abietic acid, methyl abietate alcohol, abietic alcohol, abietyl alcohol, Dertomal™ 18, Abitol™, Hercolyn™ D, Foral® 105, Staybelite® 10, Granolite™ SG, Dercolyte™ ZS, Dertophene™ 18
Other substances to which the patient may react:Wood tars, other coniferous trees, other plant materials including Chrysanthemum, some spices, fragrances, oils
Found in:Cosmetics, adhesives, a variety of household and industrial products


8. Epoxy resin

Concentration:0.050 mg/cm²
Allergen component per patch:Diglycidylether of bisphenol A, 0.032 mg
Vehicle:Hydroxypropyl cellulose
Synonyms and/or components:4,4′-Isopropylidenediphenol-epichlorohydrin, diglycidyl ether, bisphenol A [2,2-bis(4-hydroxyphenyl)propane] (diphenylpropane), epichlorohydrin (1-chloro-2,3-epoxypropane) (8-chloropropylene oxide)
Other substances to which the patient may react:The hardening agent of a two-part adhesive, specifically components such as ethylenediamine
Found in:Two-part adhesives, surface coatings, paints


9. Quinoline mix

Concentration:0.190 mg/cm²
Allergen component per patch:Clioquinol: 0.077 mg, Clorquinaldol: 0.077 mg
Synonyms and/or components:5-chloro-7-iodo-8-hydroxyquinoline
Other substances to which the patient may react:Vioform, chlorquinaldol quinoform, entroquinol, sterosan, quinaband, iodinechloridequinoline. Enterovioform (R)
Found in:Paste bandages, medicated creams and oinments


10. Balsam of Peru

Concentration:0.80 mg/cm²
Allergen component per patch:Balsam of Peru, 0.65 mg total
Synonyms and/or components:Synonyms: balsamum peruvianim, Peruvian balsam, Indian balsam, China oil, black balsam, Honduras balsam, Surinam balsamComponents or chemically related allergens: Cinnamic acid, benzyl salicylate, vanillin, benzoic alcohol, benzyl acetate, benzaldehyde, benzyl benzoate and other benzoates, benzoic acid, cinnamic alcohol, cinnamic aldehyde, cinnamyl cinnamate, methylcinnamate, eugenol, isoeugenol, coniferyl alcohols, resinous substances.
Other substances to which the patient may react:Cinnamein (essential oil), oil of cinnamon, tincture of krameria, balsam of Copaiba, storax (styrax), essence of orange peel, spices (e.g., Jamaican pepper, cinnamon, cloves, nutmeg, paprika, curry, vanilla), Tiger Balm® (oriental), benzoin tincture (gum benzoin), wood tars, colophony, balsam of Tolu, turpentine, beeswax, coumarin, diethylstilbestrol, propolis
Found in:Foods, cosmetics, fragrances, flavorings, topical medications


11. Ethylenediamine dihydrochloride

Concentration:0.050 mg/cm²
Allergen component per patch:Ethylenediamine, 0.018 mg
Synonyms and/or components:1,2-Ethanediamine, 1,2-diaminoethane, chlorethamine
Other substances to which the patient may react:Aminophylline, hydroxyzine, piperazine-based antihistamines (meclizine, buclizine, chlorcyclizine, cyclizine), tripelennamine, promethazine HCl, epoxy resin catalysts (ethylenediamine and chemically related amines such as diethylenediamine, dipropylenetriamine, triethylenetetramine, tetraethylenetetramine, trimethylhexamethylenediamine)
Found in:Topical medications, eyedrops, industrial solvents, anticorrosive agents


12. Cobalt dichloride

Concentration:0.020 mg/cm²
Allergen component per patch:Cobalt, 0.0040 mg
Vehicle:Hydroxypropyl cellulose
Synonyms and/or components:Cobalt blue, cobaltous (modifying any word)
Alloys containing cobalt:Stellite®, Vitallium®, Alnico™, Durlium™, Mobilium™, Permalloy™, Ticonium®, Wolfram™ carbide
Other substances to which the patient may react:Nickel, chromate
Found in:Metal-plated objects, paints, cement, vitamin B12


Patch testing (Panel 2)
13. p-tert-butylphenol formaldehyde resin

Concentration:0.050 mg/cm²
Allergen component per patch:p-tert-Butylphenol formaldehyde, 0.041 mg
Vehicle:Hydroxypropyl cellulose
Synonyms and/or components:Paratertiary butylphenol formaldehyde resin, PTBP formaldehyde, butylphen, 4(1,1-dimethylethyl)phenol
Other substances to which the patient may react:Degaplast™ glue, neoprene adhesives
Found in:Waterproof glues, bonded leather, construction materials, paper, fabrics


14. Paraben mix

Concentration:1.00 mg/cm²
Allergen component per patch:Methyl p-hydroxybenzoate, 0.162 mg;
ethyl p-hydroxybenzoate, 0.162 mg;
propyl p-hydroxybenzoate, 0.162 mg;
butyl p-hydroxybenzoate, 0.162 mg;
benzyl p-hydroxybenzoate, 0.162 mg;
Synonyms and/or components:Methylparaben, ethylparaben, propylparaben, butylparaben, p-hydroxybenzoate, p-hydroxybenzoic acid, Nipagin®, Perservaben™, Protaben™, Aseptoform™, Lexgard®, Parasept®, Liqua Par®, Germaben™ II (mixture), Nipastat® (mixture), Phenonip® (mixture), undebenzofene-C (mixture)
Other substances to which the patient may react:p-Aminobenzoic acid (PABA) esters, p-phenylenediamine (rarely)
Found in:Preservative in topical formulations, cosmetics, foods, industrial preparations


15. Carba mix

Concentration:0.25 mg/cm²
Allergen component per patch:Diphenylguanidine, 0.067 mg;
zincdibutyldithiocarbamate, 0.067 mg;
zincdiethyldithiocarbamate, 0.067 mg;
Vehicle:Hydroxypropyl cellulose
Synonyms and/or components:Carbamate, carbanilate, 1,3-diphenylguanidine/(DPG™, Nocceler™ D, Sanceler™ D, Soxinol® D), zincdibutyldithiocarbamate (ZBC, butazin, butyl zimate, Nocceler™ BZ, Soxinol® BZ, Butazate®, Butasan®), zincdiethyldithiocarbamate (ZDC™, ZDEC™, Etazin™, Ethasan™, ethyl zimate, Nocceler™ EZ, Soxinol® EZ, Ethazate®)
Other substances to which the patient may react:Thiuram mix, mercapto mix, mercaptobenzothiazole, disulfiram (Antabuse®).
Found in:Rubber products, glues for leather, pesticides, vinyl, soaps, shampoos, disinfectants


16. Black rubber mix

Concentration:0.075 mg/cm²
Allergen component per patch:N-Isopropyl-N’-phenyl paraphenylenediamine, 0.0102 mg; N-cyclohexyl-N’-phenyl paraphenylenediamine, 0.0255 mg; N,N’-diphenyl paraphenylene-diamine, 0.0255 mg
Synonyms and/or components:N-Phenyl-N’-cyclohexyl-p-phenylenediamine (CPPD): phenylcyclohexyl PPD, Flexzone™ GHN-Isopropyl-N’-phenyl-p-phenylenediamine (IPPD): isopropyl 0 PPD, Akrochem® Antioxidant PD1, ANTO’H’™, Flexzone™ 3-C, Permanex™ IPPD, Santoflex® IPN,N’-Diphenyl-p-phenylenediamine (DPPD): Diphenyl® PPD
Other substances to which the patient may react:Hair dye chemicals: p-aminodiphenylamine, p-phenylenediamine
Found in:All black rubber products, some hair dyes


17. Cl+ Me- Isothiazolinone

Concentration:0.0040 mg/cm²
Allergen component per patch:5-Chloro-2-methyl-4-isothiazolin-3-one, 0.0024 mg; 2-methyl-4-isothiazolin-3-one, 0.0008 mg
Synonyms and/or components:Methylchloroisothiazolinone (MCI), methylisothiazolinone (MI), Kathon®
Other substances to which the patient may react:Other isothiazolinones
Found in:Cosmetics and skin care products, topical medications, household cleaning products; as Kathon® in industrial products


18. Quaternium-15

Concentration:0.100 mg/cm²
Allergen component per patch:Quaternium-15, 0.081 mg
Vehicle:Hydroxypropyl cellulose
Synonyms and/or components:N-(3-chloroallyl)-Hexaminium chloride, cis-1-(3-chloroallyl)-3,5,7-triaza-1-azonium-adamantane chloride, 1-(3-chloroallyl)-3,5,7-triaza-1-azonium-adamantane chloride, Preventol® D 1, methanamine-3-chloroallylochloride, chloroallyl methanamine chloride, Dowicil® 75 (or 100 or 200), azonium-adamantane chloride
Other substances to which the patient may react:Formaldehyde:Formaldehyde-releasing preservatives found in cosmetics and topical agents: Germall® 115 (imidazolidinyl urea), Germall® II (diazolidinyl urea), Glydant® [DMDM (dimethylolmethyl) hydantoin], Bronopol™ (2-bromo-2-nitropropane-1,3-diol), Tris Nitro® [tris (hydroxymethyl) nitromethane]Formaldehyde-releasing preservatives found in industrial and metal-working fluids: Dowicil® 75, Tris Nitro®, Grotan™ HD2, Grotan™ BK, Triadine®-10, Onyxide™ 200, Vancide™ TH, Myacide™ BT
Found in:preservative in cosmetics and skin care products, household polishes and cleaners, industrial products


19. Mercaptobenzothiazole

Concentration:0.075 mg/cm²
Allergen component per patch:Mercaptobenzothiazole, 0.061 mg
Synonyms and/or components:MBT, 2-benzathiazalethiol, Captax®, Dermacid™, Mertax™, Thiotax®, Nocceler™ M, Rotax®
Other substances to which the patient may react:Mercapto mix, thiuram mix, carba mix
Found in:Rubber products, adhesives, industrial products, veterinary tick/flea sprays and powders, film emulsion


20. p-Phenylenediamine

Concentration:0.090 mg/cm²
Allergen component per patch:p-Phenylenediamine, 0.073 mg
Synonyms and/or components:Paraphenylenediamine (PPD or PPDA), 1,4-benzenediamine, 1,4-phenylenediamine, Rodol™ D, p-aminoaniline, Orsin™, p-diaminobenzene, Ursol™ D
Other substances to which the patient may react:PABA-based sunscreens or creams, other dye chemicals, Azo® or disperse textile dyes, p-aminosalicylic acid, black rubber products, diaminodiphenylmethane (epoxy hardener), p-toluenediamine, p-aminodiphenylamine, 2,4-diaminoanisole, o-animophenol
Occasionally, ‘sulfa’ drugs (sulfonamides), ‘caine’ drugs such as benzocaine
Found in:Permanent (coal tar) or semipermanent hair dyes, dyed textiles, cosmetics, printing ink, photodeveloper


21. Formaldehyde

Concentration:0.18 mg/cm²
Allergen component per patch:Formaldehyde, 0.15
Synonyms and/or components:Oxymethylene, methanal, formalin
Formaldehyde-releasing preservatives:Preservatives found in cosmetics and topical agents: Quaternium-15, Germall® 115 (imidazolidinyl urea), Germall II® (diazolidinyl urea), Glydant® [DMDM(dimethylolmethyl) hydantoin], Bronopol™ (2-bromo-2-nitropropane-1,3-diol), Tris Nitro® [tris (hydroxymethyl) nitromethane]Preservatives found in industrial and metal-working fluids: Dowicil® 75, Tris Nitro®, Grotan™ HD2, Grotan™ BK, Triadine®-10, Onyxide™ 200, Vancide™ TH, Myacide™ BT.
Found in:Fabric finishes, cosmetics, plastics, synthetic resins, glues, textiles, construction material


22. Mercapto mix

Concentration:0.075 mg/cm²
Allergen component per patch:N-Cyclohexylbenzothiazyl-sulfenamide, 0.0203 mg; dibenzothiazyl disulfide, 0.0203 mg; morpholinylmercaptobenzothiazole, 0.0203 mg
Synonyms and/or components:N-Cyclohexyl-2-benzothiazole-sulfenamide (CBTS, CBS): cyclohexylbenzothiazyl-sulphenamide, Durax®, Santocure®
Dibenzothiazyl disulfide: 2,2′-benzothiazyl disulfide, Altax®, Thiofide®, Naugex® MBT, Vulkacit® DM
Morpholinylmercaptobenzothiazole (MOR, MMBT): 4-morpholinyl-2-benzothiazyl disulfide
Other substances to which the patient may react:Mercaptobenzothiazole, carba mix, thiuram mix
Found in:Rubber products, glues for leather and plastics, industrial products


23. Thiomersal

Concentration:0.0080 mg/cm²
Allergen component per patch:Thiomersal, 0.0065 mg
Vehicle:Hydroxypropyl cellulose
Synonyms and/or components:Merthiolate®, Mercurochrome®, sodium ethylmercurithiosalicylate, mercurothiolate, merzonin, mertorgan, merfamin, ethyl (2-mercaptobenzoato-S) mercury (sodium salt), thiomersalate, thiomersal, thiomersalan, [(o-carboxyphenyl)thio] ethylmercury (sodium salt)
Other substances to which the patient may react:Other organic (not metallic) mercury compounds, piroxicam (Feldene®)
Found in:Preservative in contact lens solutions, cosmetics, nose and ear preparations, injectable drugs


24. Thiuram mix

Concentration:0.025 mg/cm²
Allergen component per patch:Tetramethylthiuram monosulfide, 0.0051 mg; tetramethylthiuram disulfide, 0.0051 mg; disulfiram, USP, 0.0051 mg; dipentamethylenethiuram disulfide, 0.0051 mg
Synonyms and/or components:Tetramethylthiuram monosulfide (TMTM)Tetramethylthiuram disulfide (TMTD): Thiram™, thiurad, Thiosan™, Thylate®, Thiuramyl™, Tiuramyl™, Puralin™, Fernasan™, Nomersan™, Rezifilm®, Pomarsal™, Tersan®, Tuads®, Tulisan™, Arasan®Disulfiram: Antabuse®, bis(diethylthiocarbamoyl) disulfide, tetraethylthiuram disulfide (TETD), Cronetal™, Abstenisil™, Stopetyl™, Contralin™, Robac™ TET, Antadix™, Antiethanol™, ethyl thiurad, Etabus™, Rosulfiram™, Abstinyl™, Thiuranide™, Tetradine™, Noxal™

Dipentamethylenethiuram disulfide (PTD): Robac™ PTD

Other substances to which the patient may react:Mercapto mix, mercaptobenzothiazole, carba mix
Found in:Rubber products, adhesives, pesticides, gloves, drugs
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