Contact Dermatitis-Allergic


  • Prevalence: represents about 20% of cases of contact dermatitis
  • Negative Correlation with Presence of Atopy: most studies denonstrate a decreased prevalence of allergic contact dermatitis in atopic patients



  • Balsam of Peru
    • Fragrance Commonly Used in Sunscreens/Shampoos
  • Benzothiazoles
    • Rubber Additive: used in boots, shoes, and gloves
  • Carbamates
    • Rubber Accelerator
  • Ethylenediamine
    • Dyes
    • Medications
  • Formaldehyde (see Formaldehyde, [[Formaldehyde]])
  • Lanolin
  • Mercaptobenzothiazole
    • Rubber Accelerator
  • Paraphenylenediamine (PPD) (see Paraphenylenediamine, [[Paraphenylenediamine]])
    • General Comments
      • PPD is a derivative of aniline
      • PPD is colorless, but is easily oxidized substance and is converted to the allergenic hapten when it is partially oxidized into an intermediate state in the epidermis/dermis
    • Hair Dyes
    • Inks
    • Photographic Chemicals
    • “Black” Henna Tattoos: while sensitivity to normal brown henna is uncommon, PPD may be added to henna tattoos to darken the color and reduce their fixation times
      • FDA has prohibited use of PPD on the skin
  • Potassium Dichromate
    • Anti-Rust Products
    • Cements
    • Household Cleaners
    • Leather
    • Matches
    • Paints
  • Quaternium-15
    • Formaldeyde-Releaser
  • Thiurams
    • Rubber Accelerator
    • Paints
    • Pesticides


  • Aminoglycosides (see Aminoglycosides, [[Aminoglycosides]])
  • Aminophylline (see Aminophylline, [[Aminophylline]])
  • Bacitracin (see Bacitracin, [[Bacitracin]]): topical
  • Benzocaine (see Benzocaine, [[Benzocaine]]): topical
    • Common etiology
  • Corticosteroids (see Corticosteroids, [[Corticosteroids]]): topical
    • May be a reaction to the steroid itself or to a preservative
  • Dibucaine: topical
    • Epidemiology: rare etiology
  • Lidocaine (see Lidocaine, [[Lidocaine]]): topical
    • Epidemiology: rare etiology
  • Mepivacaine (see Mepivacaine, [[Mepivacaine]]): topical
    • Epidemiology: rare etiology
  • Neomycin (see Neomycin, [[Neomycin]]): topical
    • Epidemiology: common etiology
  • Tetracaine (see Tetracaine, [[Tetracaine]]): topical
    • Epidemiology: common etiology
  • Thimerosal (see Thimerosal, [[Thimerosal]]): preservative used in vaccines and ocular/ear/nasal medications


  • Chromium (see Chromium, [[Chromium]]): present in jewelry
  • Cobalt (see Cobalt, [[Cobalt]])
  • Gold (see Gold, [[Gold]]): present in jewelry
  • Mercury (see Mercury, [[Mercury]]): organic forms
  • Nickel Sulfate (see Nickel, [[Nickel]]): present in earrings, buckles, zippers, buttons, metal clips, and metal alloys
    • Epidemiology: most common allergen in most studies
      • Most common metal allergen in the US
      • More common in females


Anacardiaceae Family-Toxicodendron Genus Plants (aka Rhus Dermatitis)

  • Epidemiology: >70% of the US population is sensitized to these plants
  • Types
    • Brazilian Pepper Tree (Schinus Terebinthifolius): due to exposure to sap from tree
    • Cashew Nuts (Tree: Anacardium occidentale): due to ingestion of cashew nut butter or cashew nuts contaminated with cashew nut shell oil (cashew nut shell oil contains the allergens, cardanol, cardol and anacardic acid, which would normally be inactivated by proper roasting)
      • Note: cashew nuts are also associated with anaphylaxis (via a type I hypersensitivity reaction) -> in this case, anaphylaxis occurs due to a low molecular weight substance in the kernel itself (and cross-reactivity with pistachio nuts may occur)
    • Ginkgo Biloba Fruit/Nuts (see Ginkgo Biloba, [[Ginkgo Biloba]]): due to exposure to fruits/nuts from tree (especially those from female trees)
    • Mango Fruit (Tree: Mangifera indica): mango fruit-asssociated contact dermatitis usually occurs in perioral region of face (cheilitis) or hands due to contact with the peel, rather than the juice
    • Mango Tree (Mangifera indica): due to exposure to sap from tree
    • Poison Ivy (Toxicodendron radicans or Rhus radicans)/Western Poison Ivy (Toxicodendron rydbergii or Rhus rydbergii) (see Toxicodendron Radicans, [[Toxicodendron Radicans]]): due to exposure to plant itself
      • Smoke from burning plants may result in severe dermatitis
    • Poison Sumac (Toxicodendron vernix or Rhus vernix) (see Toxicodendron Vernix, [[Toxicodendron Vernix]]): due to exposure to plant itself
      • Smoke from burning plants may result in severe dermatitis
    • Western Poison Oak (Toxicodendron diversilobum or Rhus diversiloba)/Atlantic Poison Oak (Toxicodendron pubescens or Rhus toxicarium) (see Toxicodendron Diversilobum, [[Toxicodendron Diversilobum]]): due to exposure to plant itself
      • Smoke from burning plants may result in severe dermatitis
  • Mechanism: exposure to the oleoresin, urushiol (which contains the antigen, pentadecylcatechol)

Asteraceae Family (aka Compositae Family, aka Aster Family, aka Daisy Family, aka Sunflower Family) Plants (aka Ragweed or Parthenium Dermatitis)

  • Aster: Greek for star (the plants in this family have star-shaped flowers)
  • Epidemiology: mainly occurs in middle-aged and elderly adults during the summer months (but either sex and any age group may be affected at any time of year)
  • Types (there are over 20,000 species in this family)
    • Absinthe (Artemisia absinthium): from the wormwood genus
    • Ambrosia (Ragweed)
    • Arnica
    • Aster
    • Chamomile-German (Matricaria recutita)/Chamomile-Roman (Chamaemelum nobile)
    • Chicory (Cichorium intybus)
    • Chrysanthemum (Chrysanthemum coronarium): edible variety
    • Daisy (Bellis perennis): common European daisy (name is derived from “dæges eage”, which means “day’s eye,” as the petals open at dawn and close at dusk)
    • Dandelion (Taraxacum)
    • Echinacea (Echinacea purpurea): used medicinally
    • Feverfew (Tanacetum parthenium) (see Feverfew, [[Feverfew]])
    • Globe Artichoke (Cynara scolymus)
    • Guayule (Parthenium argentatum): source of hypoallergenic latex
    • Lettuce (Lactuca sativa): used as food item
    • Marigold (Calendula): used in herbal teas and potpourri
    • Ragweed (Ambrosia): pollen from this plant is the leading case of “hay fever” in the US
    • Safflower (Carthamus tinctorius): oil is used in cooking
    • Sunflower (Helianthus annus)
    • Tarragon (Artemisia dracunculus): from the wormwood genus
  • Mechanism: exposure (via multiple routes) to sesquiterpene lactones (which are present in the oleoresin of leaf, stem, flower and possibly, the pollen): such as parthenolide, etc
    • Airborne Exposure
    • Direct Exposure to the Plant, Pollen, or Products Made from Plant Extracts
    • Ingestion of Plant Extracts (for example: echinacea in herbal medicines)


  • Type IV Delayed Hypersensitivity Reaction: requires prior sensitization to antigen (either directly via skin contact or inhalational exposure)
    • Induction Phase: allergen (hapten) penetrates epidermis -> processing by antigen-presenting cell (Langerhans cells, dermal dendrocytes, macrophages) -> processed antigen is presented to T-cells -> T-cell expansion in lymph nodes -> differentation into memory T-cells and effector T-cells (which are released into circulation)
    • Elicitation Phase (requires hours to develop): repeat exposure to antigen -> antigen penetrates epidermis -> processed by antigen-presenting cells -> presentation to T-effector cells -> lymphokine production -> allergic contact dermatitis
  • Systemic Contact Dermatitis: subset of allergic contact dermatitis where a patient who is allergen sensitized (typically via cutaneous exposure) is later exposed to the same allergen (or a cross-reacting molecule) via a systemic route (oral, transcutaneous, transmucosal, intravenous, intramuscular, or inhalational)
  • Concentration of Agent: less critical to pathogenesis than in irritant contact dermatitis
  • Pruritus: mediated by specific itch fibers at the dermo-epidermal junction


Patch Skin Testing

  • Sensitivity: often diagnostic
  • Selection of Antigens: About 30 allergens are responsible for 80% of cases
    • Sesquiterpene Lactone Mix: used to test for Compositae contact dermatitis
  • Technique
    • Chambers are placed on the back with adhesive and left in place for 48 hrs: patients may return for additional readings at 72 or 96 hrs to determine the presence of delayed responses (this is especially important for cases of suspected corticosteroid-induced dermatitis)
    • Avoid performing during widespread active dermatitis or while on systemic steroids

Skin Biopsy

  • Typically nonspecific and less useful than patch testing
  • Allergen-Specific T-Cells: may be found in skin biopsy

Allergen-Specific T-Cells in Blood (ELISPOT)

  • Enzyme-linked immunospot testing

Clinical Manifestations

  • Reaction Latency After Contact: several hours to 5-6 days
    • Clinical symptoms occur hours-days after the repeat exposure (since elicitation phase requires hours to progress)
  • Geographic Pattern
    • Sharp demarcation may occur in some cases: mimicking the geopgraphic pattern observed in irritant contact dermatitis
    • May not be limited to the contact site
  • Variable Presentation: typically pruritic and may present with any of the following

Contact Dermatitis

Systemic Contact Dermatitis

  • Baboon Syndrome (most recognizable form of systemic contact dermatitis): diffuse, well-demarcated erythema of buttocks, upper inner thighs, and axillae
    • Baboon syndrome caused by systemic medications without a known history of prior cutaneous sensitization is called drug-related baboon syndrome (DRBS) or symmetric drug-related intertriginous and flexural exanthema (SDRIFE)
    • Etiology of SDRIFE
      • Aminopenicillins
      • β-lactams
      • Certain chemotherapeutic agents
    • Criteria for SDRIFE
      • Exposure to systemic drug at first or repeated dose
      • Erythema of the gluteal/perianal area and/or V-shaped erythema of the inguinal area
      • Involvement of at least one other intertriginous localization
      • Symmetry of affected areas
      • Absence of systemic toxicity
  • Dermatitis at Sites of Previous Exposure to Allergen: at previous sites of dermatitis or at sites of previous positive patch tests
  • Dyshidrotic Hand Eczema
  • Flexural Dermatitis
  • Exanthematous Rash (see Exanthems, [[Exanthems]])
  • Erythroderma (see Erythroderma, [[Erythroderma]])
  • Vasculitis-Like Lesions (see Vesicular-Bullous Skin Lesions, [[Vesicular-Bullous Skin Lesions]])


  • Latency to Resolution: typically takes many days to resolve: Rhus dermatitis may persist for 7-21 days (rarely persists for >40 days)
  • Topical Steroids: usually effective
  • Systemic Steroids: may be required in severe cases -> taper over 2-3 weeks
  • Azathioprine (see Azathioprine, [[Azathioprine]])
  • Degree of Sensitivity: may wain over time or remain present throughout life

Photo Contact Dermatitis


  • Citrus Family
    • Limes: exposure is most common when limes are used in beverages, when juice runs down arm or neck -> sun exposure produces linear streaks
  • Mulberry Family
    • Figs
  • Perfumes: common soure of photo contact dermatitis
  • Umbelliferae Family
    • Parsnip
    • Celery
  • Drugs
    • Sulfonamides (see Sulfonamides, [[Sulfonamides]])
    • Fluoroquinolones (see Fluoroquinolones, [[Fluoroquinolones]])
    • Tetracyclines (see Tetracyclines, [[Tetracyclines]])
    • Oral Contraceptives (see Oral Contraceptives, [[Oral Contraceptives]])
    • NSAID’s (see NSAID’s, [[NSAID]]): ketoprofen, ibuprofen, suprofen, tiaprofenic acid, diclofenac, etofenamate, piroxicam, indomethacin, benzydamine
    • Sunscreens
    • Topical Cold Tar Extract


  • Dermatitis which occurs due to substances which require photo conversion to either a photoallergen (producing a type IV hypersensitivity-type allergic dermatitis) or phototoxic substance (producing an irritant dermatitis)
  • Transformation is usually light wavelength-specific for each substance (requiring specific exposure to either UV-A, UV-B, or white light)

Clinical Manifestations

  • Geographic Distribution: typically only occurs on sun-exposed areas (face, arms, and upper chest)
    • Skin under the chin, behind the ears, and on the upper eyelids is typically spared

Contact Urticaria


  • Contact urticaria due to the common stinging nettle (Urtica dioica)–histological, ultrastructural and pharmacological studies. Clin Exp Dermatol. 1991 Jan;16(1):1-7
  • Compositae dermatitis. Australas J Dermatol. 1999 Aug;40(3):123-8 [MEDLINE]
  • Long-term safety and toxicity of azathioprine in patients with air-borne contact dermatitis. Indian J Dermatol Venereol Leprol. 2001 Mar-Apr;67(2):75-7 [MEDLINE]
  • Contact allergy to herbal teas derived from Asteraceae plants. Contact Dermatitis. 2006 Apr;54(4):196-201 [MEDLINE]
  • Compositae dermatitis from airborne parthenolide. Br J Dermatol. 2007 Mar;156(3):510-5
  • A systematic approach to systemic contact dermatitis and symmetric drug-related intertriginous and flexural exanthema (SDRIFE): a closer look at these conditions and an approach to intertriginous eruptions. Am J Clin Dermatol. 2011 Jun 1;12(3):171-80 [MEDLINE]