Version May 2023
INTRODUCTION — Allergic contact dermatitis is the classic presentation of a T cell-mediated, delayed-type hypersensitivity response to exogenous agents and the most frequent occupational skin disease. Health professionals, chemical industry workers, beauticians and hairdressers, machinists, and construction workers have the highest risk of developing occupational allergic contact dermatitis. However, exposure to common industrial allergens may also occur at home.
This topic will review the agents that most commonly cause allergic contact dermatitis. The pathogenesis, diagnosis, and treatment of allergic contact dermatitis are discussed separately.
●(See "Basic mechanisms and pathophysiology of allergic contact dermatitis".)
●(See "Clinical features and diagnosis of allergic contact dermatitis".)
●(See "Patch testing".)
●(See "Management of allergic contact dermatitis".)
METALS — Hypersensitivity reactions to metals are common [1]. Nickel, cobalt, gold, and chromium are the most prevalent metal allergens, since they are used in a wide range of everyday items, medical devices, and industrial applications. Co-reactions to metals often occur and should not be considered cross-reactions [2]. Nickel and other metals released by implanted medical devices may cause an allergic contact dermatitis over the implant site or a systemic reaction. Allergic reaction to implanted metals are rarely cause of chronic pain, implant loosening, or failure [3]. Criteria for diagnosing hypersensitivity reactions in implant devices have been proposed and are summarized in the table (table 1) [4-6]. The American Contact Dermatitis Society published management suggestions for both pre- and post-metal-implant patients [7].
Nickel is a ubiquitous allergen. In a cross-sectional analysis of over 44,000 patients patch tested by the North American Contact Dermatitis Group from 1994 to 2014, the average frequency of nickel sensitivity was 17.5 percent, and 55.5 percent of reactions were thought to be clinically relevant [8]. Women react more frequently to nickel. Sensitization to nickel has been shown to correlate with number of body piercings [9]. It is present in jewelry, kitchen tools and silverware, clothing, and food. Avoidance of costume jewelry, metal fasteners, and other metal objects is usually sufficient for most nickel-allergic patients. In extremely sensitive individuals, nickel ingestion with foods (eg, chocolate, nuts, oats, green beans, peas, canned foods) may cause systemic allergic contact dermatitis or, in rare cases, chronic urticaria [10]. Avoidance of nickel in implanted medical devices is controversial. Preimplant testing is not indicated for all individuals, only for those with a significant history of dermatitis where metal touches the skin. Postimplant testing is indicated if metal allergy is suspected as a cause of device malfunction/failure [7]. External contact with nickel may occur through stainless steel instruments as well as many skin staples [3].
Systemic reactions to ingested nickel, defined as systemic nickel allergy syndrome (SNAS), is a rare syndrome associated with dietary nickel exposure. Approximately 6 percent of nickel-allergic individuals react to gastrointestinal nickel exposure and may benefit from a restricted nickel diet [11,12].
Cobalt is a co-reactor with nickel and an allergen itself. It has a blue color and can be found in cosmetics, especially eye makeup, and blue tattoo pigments. Other potential sources of exposure to cobalt include wet clay (pottery), plastics manufacturing, bricklaying and other industrial works, and some hair dyes. Surgical stainless steel and the cobalt-chrome-molybdenum alloys used in orthopedic implants have high cobalt content.
Chromium is also a ubiquitous allergen. It is the fourth most common material in the crust of the earth and is present in both the soil and the water [2]. Chromium is used in the industry (eg, cement, leather tanning, paints), in various types of stainless steel, and as a green coloring agent in soaps, cosmetics, and tattoo pigments. Chromium is also present in some foods, with the highest concentrations in brewer's yeast, beef, liver, thyme, black pepper, and cloves, and in dietary supplements [2].
Gold in precious jewelry may cause allergic contact dermatitis, most often involving the hands, face, and eyelids [13-15]. Some patients with a positive patch test to gold, however, may tolerate wearing gold jewelry without problem. Gold dental restorations may be associated with positive patch test reactions to gold in the absence of clinical signs of allergic contact dermatitis or intraoral disease. In one study, approximately 30 percent of asymptomatic individuals with gold dental restorations had a positive patch test to gold [15].
PRESERVATIVES — The two main groups of preservatives used to prevent bacterial and fungal spoilage in topical preparations, cosmetics, and personal care products are formaldehyde/formaldehyde releasers and nonformaldehyde agents.
Formaldehyde/formaldehyde releasers — Formaldehyde is a contact sensitizer classified as a known human carcinogen by the International Agency for Research on Cancer. Formaldehyde itself is generally not added to consumer products and is rarely listed on labels in the United States and the European Union, but many chemicals used as preservatives degrade over time and release formaldehyde into the product. Cross-reactions may occur between formaldehyde and all the formaldehyde releasers, which are allergens also in their undegraded state. There are regulations in both the United States and the European Union restricting work-place and environmental exposures to formaldehyde [16,17].
Cosmetics and personal care products that may contain formaldehyde include nail polishes, makeup, body washes, deodorants, and shampoos. Of particular concern is formaldehyde exposure among users of popular hair straightening products (also known as hair relaxers) [18-21]. Rates of formaldehyde releaser allergy have significantly decreased in the last decade [22].
Common preservatives that cause allergic contact dermatitis are listed in the table (table 2) [1]. The most common formaldehyde releasers used in consumer products are discussed below:
●Quaternium-15 – Quaternium-15 (Q15) is often present in cosmetics, personal care products, and in some metalworking cutting fluids. In 2003, it was the ninth most common preservative used in the United States and was found in 516 products [23]. Q15 was the most common cause of allergic contact dermatitis to preservatives, but it was overtaken by methylchloroisothiazolinone (13.4 percent) and iodopropynyl butylcarbamate (3.9 percent) in 2015/2016 data [24]. According to the North American Contact Dermatitis Group's 2015 to 2016 data, 3.6 percent (4.8 percent in the 2013/2014 data) of patch-tested patients react to Q15 [25]. Q15 may occasionally cross-react with other quaternary ammonium compounds, such as benzalkonium chloride, often present in eye and ear preparations.
●Imidazolidinyl urea – Imidazolidinyl urea is the third most common preservative used in the United States and is present in over 2000 cosmetic and personal care products, including baby lotions, shampoos, conditioners, and deodorants [23]. At the concentration used in cosmetics (0.03% to 0.2%), imidazolidinyl urea releases free formaldehyde at a level of approximately 5 parts per million (mg/kg) [23]. This level can be tolerated by most formaldehyde-allergic patients.
●Diazolidinyl urea – Diazolidinyl urea is used in many personal care products, often in combination with parabens (see 'Parabens' below). Sources and cross-reactions are the same as imidazolidinyl urea.
●DMDM hydantoin – 1,3-dimethylol-5,5-dimethyl (DMDM) hydantoin is widely used in shampoos, and may also be found in other personal-care products [23]. The amount of formaldehyde released depends upon the concentration and presence of protein in the product, and ranges from approximately 40 to 500 parts per million (mg/kg) [26,27]. Sources and cross-reactions are the same as for imidazolidinyl urea.
●2-bromo-2-nitropropane-1,3-diol – Although infrequently used, 2-bromo-2-nitropropane-1,3-diol (Bronopol) may be a cause of allergic contact dermatitis. Products containing Bronopol include body-cleansing products, in particular baby wipes.
Other preservatives
Isothiazolinones — Methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI) are commonly used preservatives and an important cause of product-related allergic contact dermatitis. Rates of MCI/MI allergy among patch-tested patients have significantly increased over the years, from 2.8 percent in 2005/2006, to 5 percent in 2011/2012 [22], 6.4 percent in 2013/2014, 7.3 percent in 2015/2016 [24], and 11 percent in 2017/2018 [28]. In a series of 703 patients tested between December 2014 and January 2015, the prevalence of positive reactions to MCI/MI was 8 percent [29]. MI tested alone reacted in 13.4 percent of tested individuals during 2015 to 2016 [24] and increased to 15.3 percent in 2017 to 2018 data [28].
Exposure sources include wash-off personal care products, such as hair care products and body washes, moisturizing creams/lotions, premoistened toilet wipes [30], and laundry detergents. MI was tested by the North American Contact Dermatitis Group for the first time in 2013 to 2014 with a prevalence reported at 10.9 percent, the third most common allergen after nickel and fragrances, respectively [25]. MI is also used in water-based paints. There are reports of allergic contact dermatitis from airborne exposure in recently painted indoor environments [31].
Isothiazolinones are also used in industrial applications with the trade names Kathon CG, Euxyl K100, or Grotan K. The combination of MCI and MI (Kathon CG) is a sensitizer, as are the individual agents alone. Cross-reactions with other isothiazolinones, such as benzisothiazolinone, may occur [32].
Parabens — Parabens are the most common preservatives in cosmetics and pharmaceuticals, but are the least frequent cause of allergic contact dermatitis [23,33]. They are tested in a mix of four related chemicals: methyl-4-hydroxybenzoate, propyl-4-hydroxybenzoate, ethyl-4-hydroxybenzoate, and butyl-4-hydroxybenzoate.
In addition to personal care products, parabens are also found in foodstuffs (table 3) [34,35]. However, it is uncertain whether oral avoidance of parabens is necessary in sensitized individuals [23]. Parabens may cross-react with the "para" amino group of related chemicals, such as para-phenylenediamine, the ester class of anesthetics (especially benzocaine), and sulfonamides, although the incidence of this is low [23,36]. (See 'Hair care products' below and 'Anesthetics' below.)
Methyldibromo glutaronitrile — Methyldibromo glutaronitrile is a non-formaldehyde-based preservative with activity against fungi, bacteria, and yeasts. In the past, it was widely used in both the United States and in the European Union in leave-on products, often mixed with phenoxyethanol (Euxyl K400). It was also used in products for industrial use (eg, cutting fluids, coolants, glues and adhesives).
Common sources include facial and body lotions, cleansers and wipes, moistened toilet paper, fabric softeners, and liquid soaps. In 2007, the European Union established a "no safe use" policy for methyldibromo glutaronitrile and banned it from all personal care products. In the United States, its use is becoming less frequent, and it has been removed from some of the commercially available patch testing series.
Thimerosal — Thimerosal (sodium ethylmercury thiosalicylate) is a mercurial antiseptic and antifungal agent widely used in the past as a preservative in topical preparations, cosmetics, injectable immunoglobulins, and vaccines. Mercury-containing agents, such as thimerosal, are regulated by the United States Environmental Protection Agency and are rarely used in topical preparations both in the United States and Europe. Thimerosal may be found at low or trace concentrations in vaccines [37]. Cross-reactions include other mercurial compounds such as phenylmercuric acetate or dental amalgam.
Iodopropynyl butylcarbamate — Iodopropynyl butylcarbamate (IPBC) is a broad-spectrum bactericide and fungicide, used initially in industrial applications [38]. In the last 20 years, its use has spread into many consumer products [39]. Although the chemical structure of IPBC is similar to thiurams and carbamates used as rubber accelerators, there is controversy about true cross-reactions between these chemicals [39].
Benzoates — Benzoic acid is naturally occurring and used to produce other benzoate preservatives. It is found naturally in many fruits. Sodium, potassium, and calcium benzoate are common preservatives added to personal care products and processed foods/drinks [40]. As benzoates are naturally occurring in balsam of Peru, these haptens occasionally cross-react on patch testing.
FRAGRANCES — Allergy to fragrance-related chemicals is common. Perfumes and scented personal care products (eg, body washes, hair care products, moisturizing lotions) are obvious sources of exposure. However, many products that are apparently unscented may contain a masking fragrance. Labels indicating "fragrance free" or "unscented" are not always safe for a fragrance-allergic individual to use.
Fragrance allergens and ingredients commonly tested in patch test screening include:
●Fragrance mix 1 (cinnamic alcohol, cinnamic aldehyde, hydroxy citronellal, amyl cinnamaldehyde, geraniol, eugenol, isoeugenol, and oakmoss absolute).
●Fragrance mix 2 (Lyral, Citral, citronellol, farnesol, coumarin, cinnamic aldehyde).
●Myroxylon pereirae, also known as balsam of Peru.
●Limonene and linalool, fragrances that are being used more frequently in personal care products as well as in perfume/colognes.
●Jasmine and peppermint are fragrance allergens that were considered distinct enough haptens to be included separately on the allergen screening trays in the United States [41].
Patients with a suspected reaction to fragrances should use completely fragrance-free personal care products for six to eight weeks until complete clearance of the allergic rash. Of note, "unscented" products are not necessarily fragrance free and should be avoided. After this wash-out period, a prudent use of questionable products may be tried (eg, one or two per week) to identify the cause of the allergic reaction. Lists of fragrance-free products are available from the Contact Allergen Management Program (CAMP) database. (See 'Contact Allergen Management Program' below.)
Myroxylon pereirae — Myroxylon pereirae (balsam of Peru) is one of the most common contact allergens. It is a resinous sap obtained by cutting the bark of the M. pereirae tree and is a complex blend of over 400 chemicals classified within the vanilla, cinnamon, benzoate, and eugenol groups. It is largely used in perfumes, cosmetics, flavoring agents in baked goods (vanilla, cinnamon), citrus flavored carbonated beverages, and in some spices [42,43].
Balsam of Peru may also cause systemic dermatitis by oral ingestion. Cross-reactions between balsam of Peru and common foods or spices are listed in the tables (table 4A-B). Systemic allergic dermatitis due to cinnamon ingestion limited to the eyelids may occur [44].
HAIR CARE PRODUCTS — P-phenylenediamine is an azo dye intermediate, most commonly used in permanent hair dyes as a black dye. It is also used in black rubbers, photographic developers, fabric dyes, epoxy resin curing agents, oils and greases, and gasoline. Potential cross-reactions include preservatives of the paraben family, para-aminobenzoic acid, sulfonamides (including diuretics and diabetes agents), and benzoic acid ester group anesthetics (see 'Parabens' above and 'Anesthetics' below). It is important for the patient to understand that even if the hair product is "PPD free" other phenylenediamine variants (eg, Toluene-2,5-diamine sulfate) may cause reactions.
P-phenylenediamine is often found or reported as an additive in henna and "black henna" and may cause a reaction mistakenly interpreted as henna allergy. The use of pure, uncontaminated Lawsonia inermis (henna tree) should not cause reactions in p-phenylenediamine allergic patients and may actually be a reasonable alternative as a hair dye for some patients [45]. Pure henna is an extremely rare cause of allergic contact dermatitis. Use of henna followed by indigo (Indigofera tinctoria most commonly) may provide a PPD-free alternative for black hair coloring.
Cocamidopropyl betaine is a surfactant derived from coconut oil and dimethylaminopropylamine [46]. It was originally used in "no more tears" formulations and has since been used as a foaming agent in many wash-off personal care products (eg, shampoos, body washes, toothpastes), an antistatic agent in conditioners, and an emulsifier in cosmetics. The actual allergenic molecule in cocamidopropyl betaine has not been determined. Amidoamine or dimethylaminopropylamine contamination is considered the most likely cause of allergic reactions to cocamidopropyl betaine-containing products [47].
Oleamidopropyl dimethylamine is an emulsifier and surfactant used in personal care products. It is a common ingredient and an increasingly important allergen, often linked with eyelid dermatitis [48].
Glucosides (lauryl glucoside, decyl glucoside, cetearyl glucoside, coco glucoside) are the third most common surfactant group that are used as surfactants in wash-off products, such as body cleansers and shampoos, and in some leave-on products, such as moisturizers and sunscreens. They were ranked the American Contact Dermatitis Society's contact allergen of the year in 2017 [48,49] and were added to the American Contact Dermatitis Society's recommended screening allergen series in 2020 [41].
Glyceryl thioglycolate is used in acidic permanent wave solutions, usually in the salon. A similar chemical, ammonium thioglycolate, is used in basic permanent wave solutions and causes allergic contact dermatitis at a much lower rate, although irritant reactions are common. The allergen can persist in treated hair for up to three months. The basic permanent wave solutions are also available for home use.
PROPYLENE GLYCOL — Propylene glycol is a viscous, colorless, and virtually odorless alcohol. It is an excellent vehicle, humectant, and preservative. It is commonly added to topical corticosteroid preparations to increase the penetration of corticosteroid into the epidermis and is also an ingredient of underarm deodorant products. Propylene glycol is used as a preservative and solvent for food flavoring agents (E1520). Topical exposure may cause irritant or allergic contact dermatitis and ingestion may cause systemic dermatitis and urticarial reactions [50]. Other common uses include personal lubricants and conduction gels for electrocardiography or transcutaneous electrical nerve stimulation [2]. Cross-reactions rarely occur with 1,3-butylene glycol and no clear cross-reaction occurs with polyethylene glycol.
TOPICAL MEDICATIONS
Anesthetics — Local anesthetics, particularly the benzoic acid ester group (eg, benzocaine, procaine, tetracaine) may cause allergic contact dermatitis. Benzocaine is widely used in over-the-counter preparations for itch and pain relief (eg, Vagisil, Lanacane) and as a sexual desensitizing agent. A positive reaction to benzocaine is detected in 0.5 to 4 percent of patients undergoing routine patch testing [1,51,52]. Benzocaine may cross-react with other local anesthetic agents and with para-aminobenzoic acid (PABA) derivatives such as p-phenylenediamine and PABA-based sunscreens (see "Allergic reactions to local anesthetics"). Local anesthetics of the amide group (lidocaine and others) cause allergic contact dermatitis at a lower rate.
Antibiotics — Neomycin is a topical aminoglycoside antibiotic often used in "triple antibiotic" type preparations. Positive patch test reactions to neomycin are found in approximately 9 percent of patients tested [1]. Other aminoglycoside antibiotics such as gentamicin or tobramycin may cross react with neomycin.
Bacitracin is a topical antibiotic produced by the Tracey strain of Bacillus subtilis. It is often included in the triple antibiotic products [53]. It is a common allergen, reacting in approximately 8 percent of patients tested [1,22].
Polymyxin B, which is produced by Bacillus polymyxa, can co-react with bacitracin and uncommonly causes allergic contact dermatitis itself [53]. It was added to the American Contact Dermatitis Society's screening series in 2020 [41].
Mupirocin ointment does not cross-react with bacitracin or neomycin. This may be a useful substitute for individuals needing a topical antibiotic, as it is an extremely rare cause of allergic contact dermatitis.
Corticosteroids — Topical corticosteroid preparation may induce allergic sensitization. Although vehicles and preservatives are most often the sensitizing agents, an allergic reaction to the corticosteroid itself can occur [54-57]. Topical corticosteroids have been grouped into four chemically similar, cross-reacting groups (A, B, C, D), ranked from A to D in order of decreasing potential for contact sensitization (figure 1).
Oral or parenteral corticosteroids may rarely induce a systemic contact dermatitis in individuals previously sensitized to the same corticosteroid applied topically [58]. (See "Topical corticosteroids: Use and adverse effects", section on 'Cutaneous'.)
Other — Propolis is produced by bees as an adhesive and sealant for small open spaces when building their hives. It is derived from pollens and resins of coniferous, poplar, or other trees, and is a complex mix of chemicals, containing approximately 180 different substances [59]. Propolis is largely used in traditional medicine for its antibacterial and antiinflammatory effects, and is found in many lip-care products. The main sensitizers in propolis are 3-methyl-2-butenyl caffeate and phenylethyl caffeate; benzoic, caffeic, cinnamic, coumaric, and ferulic acids are other sensitizers present in propolis [59].
Propolis may cross react with balsam of Peru, with which it shares more than 20 substances, and fragrances. Cross reaction with natural beeswax is unusual, but may occur if beeswax is contaminated with propolis. Synthetic beeswax should be safe for propolis allergic patients.
RUBBER ACCELERATORS — Rubber accelerators are chemicals used to speed the polymerization process (vulcanization) in natural latex, synthetic latex, and nonlatex rubber products. They include thiurams, carbamates, and mercaptobenzothiazoles. Thioureas, which are used in the production of neoprene, and antioxidants such as N-Isopropyl-N-phenyl-4-phenylenediamine also may cause allergy to rubber.
Thiurams and carbamates are the most common cause of accelerator allergic contact dermatitis, with a prevalence of 2.9 and 4.7 percent, respectively, according to the 2011 to 2012 patch test results of the North American Contact Dermatitis Group [22].
Thiurams most commonly screened are tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and dipentamethylene thiuram disulfide. Disulfiram, a thiuram used orally as an aversive agent in the treatment of alcohol use disorder, may cause a systemic contact dermatitis in sensitized individuals.
Carbamates are commonly tested as a carba mix, which includes 1,3-diphenylguanidine, zinc dibutyl dithiocarbamate, and zinc diethyldithiocarbamate. If carbamate allergy is strongly suspected, 1,3-diphenylguanidine should be tested separately. In addition to latex rubber products, also nitrile materials may contain carbamates. Thus, it can be extremely difficult to find carbamate-free examination or sterile surgical gloves. No clear cross-reactions between carbamates and other chemicals are known, although iodopropynyl butylcarbamate, used as a preservative in cosmetics, has been questioned as a cross-reactor.
Mercaptobenzothiazole can be found in latex and nonlatex gloves. Nitrile gloves and shoes are the most common source of exposure [45]. Mercaptobenzothiazole is also used as a corrosion inhibitor in cutting oils, antifreeze mixes, greases, adhesives, film emulsions, and in veterinary preparations such as flea and tick powders and sprays.
Dialkyl thioureas are rubber accelerators and antidegradant agents that are screened in a mix of diethyl- and dibutyl thioureas. They are used in both natural and synthetic rubber systems, as well as in adhesives, commercial paint, glue remover, detergents, fungicides, insecticides, and copy papers [45,60]. The most common sources of exposure are shoes and neoprene (polychloroprene) braces. Co-sensitization with other rubber accelerator chemicals and para-tertiary butylphenol formaldehyde resin are common, as well as cross-reactions in the thiourea group [60].
ADHESIVES
Phenol-formaldehyde resins — Para-tertiary butylphenol formaldehyde resin (PTBFR) is a synthetic polymer mainly used in adhesives. Common sources of exposure include neoprene braces, sleeves, and wetsuits and glued leather products. Other sources include motor oil, printing inks, fiberglass, plywood, and masonry sealants.
PTBFR can induce both type I and IV reactions [2]. Cross-reactions may occur with formaldehyde, resin monomer, and other formaldehyde-based resins, such as phenol formaldehyde resin, urea formaldehyde resin, melamine formaldehyde resin, and cashew nut oil-formaldehyde resin.
Colophony (rosin) — Colophony (rosin) is derived from the sap of pine trees. It is a solid residue of distillation of turpentine and its major chemical constituent is abietic acid. Rosin is commonly used in adhesives (especially some adhesive bandages), plasticizers, fabrics, asphalt/cements, chewing gum, leather cleaners, photo paper coating, mascaras, and newsprint.
Rock climbers, gymnasts, dancers, and baseball players commonly use powdered rosin to improve grip. Violinists and players of other string instruments use rosin on the bow hair. Colophony in sanitary pads may cause vulvar dermatitis [61]. Cross-reactions include balsam of Peru, turpentine, wood tars, pine resins, and propolis.
Epoxy resin — Epoxy resin systems are composed of one or more monomers, such as bisphenol A and epichlorohydrin, curing (hardening) agents, and diluents or additives. It is believed that only the monomer, but not the polymer, is allergenic. However, since the polymerization process is often incomplete, the monomer is often present in small amounts in the final product and can elicit an allergic reaction. Epoxy resin plastics and adhesives are frequently used in making sporting goods (eg, tennis rackets), vehicle parts, and in building construction. Nitrile gloves should be used for protection from epoxy resin [62].
ACRYLATES — Acrylates are used in plastics, adhesives, paints and coatings, paper finishes, dental materials, artificial nails, and many consumer products. Acrylate monomers (eg, acrylic acid, methyl methacrylate, and acrylonitrile) react to form polymers that are elastic, resistant to breaking, and transparent. Artificial nail application and nail sculpting with acrylic gels are among the most common exposures to acrylates [63-66]. In a European study, 67 percent of cases of acrylate allergic contact dermatitis were caused by nail acrylates, occurred in women in the vast majority of cases, and were associated with nonoccupational (recreational) use of cosmetic nail products in approximately one-half of the cases [67]. Facial allergic contact dermatitis may be caused by involuntary transfer of acrylates from the nails to the face [68]. In occupational settings, latex gloves do not protect from acrylates.
Ethyl acrylate and methyl methacrylate are included in many standard patch testing series. Ethyl acrylate is used in dentures and hearing aids, artificial nail products, dental fillings, glues, and inks. Methyl methacrylate is a component of orthopedic bone cement, medical adhesives, corneal contact lenses, intraocular lenses, and hearing aids. Cross-reactions between acrylates are common. However, for patients with a positive reaction to ethyl acrylate and methyl methacrylate, a more extensive patch testing may be helpful in determining which monomers can be tolerated. In a United Kingdom study, the top acrylates eliciting a positive reaction were 2-hydroxyethyl methacrylate (1.7 percent), 2-hydroxypropyl methacrylate (1 percent), and 2-hydroxyethyl acrylate (1 percent) [69].
Cyanoacrylates (ethyl-) are fast-acting glues that have many industrial applications and are also often used in artificial nail systems. They do not cross-react with ethyl acrylate or methyl methacrylate but are an important cause of allergic contact dermatitis in and of themselves [67]. The surgical wound sealer Dermabond is primarily octyl-cyanoacrylate and may cause allergic contact dermatitis reactions both on the skin as well as with internal applications. (See "Minor wound repair with tissue adhesives (cyanoacrylates)".)
Patch testing with the standard ethyl cyanoacrylate is a poor screening allergen for Dermabond allergy. Instead, octyl cyanoacrylate should be used for better screening sensitivity [70].
FABRIC DYES AND FINISHES — Disperse dyes, particularly disperse blue 106 and 124, are strong sensitizers and a common cause of contact allergy to textiles [71]. Disperse dyes are water insoluble and typically used to dye acetate and polyester fibers [72]. Cross-reactions may occur with p-phenylenediamine, an ingredient of permanent hair dyes, which is a good screening allergen for textile dye allergy [73]. (See 'Hair care products' above.)
Textile allergic contact dermatitis typically involves sites that are in close contact with clothing (eg, axilla with sparing of the vault, thighs) and is worsened by friction and sweating. In infants and young children, disposable diapers may be a source of exposure to disperse dyes [74,75].
Ethylene urea melamine formaldehyde and other formaldehyde textile resins such as dimethylol dihydroxyethyleneurea, are used as fabric finishes to prevent wrinkling, decrease shrinkage, and improve fabric strength [76]. They are usually found in "permanent press" and "wash-and-wear" type clothing and most often in fabrics that are blends of synthetic and natural fibers.
A nonevidence-based method for possibly removing formaldehyde from new clothing is soaking in dissolved powdered milk (one-quarter cup powdered skim milk dissolved in approximately 3 gallons of cold water). Clothes should be soaked for approximately 12 hours in a covered container, then rinsed well. While there are no studies proving this method is effective, it is helpful for some.
Cross- or co-reactions may occur with formaldehyde and formaldehyde-containing or releasing chemicals. (See 'Formaldehyde/formaldehyde releasers' above.)
EMERGING ALLERGENS — There are many substances that have the potential to elicit allergic contact dermatitis beyond those discussed in this topic review. The American Contact Dermatitis Society updates a suggested patch testing series that may be helpful for those looking to patch test beyond the thin-layer rapid-use epicutaneous (TRUE) test series [40]. New allergens added in 2017 were polymyxin B sulfate, lavender, sodium benzoate, ethylhexylglycerin, and benzoic acid. In 2020, 11 new allergens were added: hydroperoxides of linalool, hydroperoxides of limonene, Lyral, carmine, benzyl salicylate, disperse yellow number 3, jasmine, peppermint, pramoxine hydrochloride, shellac, and lauryl polyglucose (glucosides) [41].
ALLERGEN AVOIDANCE TIPS
Reading labels — Individuals with contact allergy should use only personal care products and prescription topicals that have a complete ingredient list included in the packaging. Ingredients are usually listed from the highest to lowest concentration and should be indicated with the accepted chemical name determined by the Personal Care Products Council. However, fragrances and flavorings are not required to be listed by specific chemical name and are often generically indicated as "fragrance."
Contact Allergen Management Program — The Contact Allergen Management Program (CAMP) of the American Contact Dermatitis Society, which requires membership, allows the clinician to create an individualized list of products that are free of specific allergens. Patients can update their list at any time by going to the CAMP website and entering codes provided with the original printout. A similar product, called the Contact Allergen Replacement Database (CARD; www.allergyfreeskin.com), is commercially available.
SUMMARY AND RECOMMENDATIONS
●Allergic contact dermatitis is a T cell-mediated, delayed-type hypersensitivity response to exogenous agents and the most frequent occupational skin disease. (See 'Introduction' above.)
●Metals, preservatives, fragrances, and topical antibiotics are the most frequent causes of allergic contact dermatitis. P-phenylenediamine, commonly used in hair dyes, is also a common sensitizer. (See 'Metals' above and 'Preservatives' above and 'Fragrances' above and 'Topical medications' above and 'Hair care products' above.)
●Avoidance is the mainstay of treatment of allergic contact dermatitis. Individuals with contact allergy should use only personal care products and prescription topicals that have a complete ingredient list included in the packaging. (See 'Allergen avoidance tips' above.)
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