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ID Reaction
Sahil Mullick, MD
Naureen Bashir Rafiq, MBBS, MD
image BASICS
A generalized skin reaction associated with various infectious (fungal, bacterial, viral, or parasitic) or inflammatory cutaneous conditions distant from the primary disease site (1)
  • “Id” is often combined with a root to reflect the causative factor (i.e., bacterid, syphilid, and tuberculid). Dermatophytid is the most frequently referenced id reaction. A dermatophytid is an autosensitization reaction in which a secondary cutaneous reaction occurs at a site distant to a primary fungal infection. The eruption typically begins within 1 to 2 weeks of the onset of the main lesion or following exacerbation of the main lesion.
  • Most commonly localized vesicular lesions, erythema nodosum, and erythema multiforme
  • System(s) affected: skin/exocrine
  • Synonym(s): dermatophytid, trichophytid, autoeczematization
  • Predominant age: all ages
  • Predominant sex: male = female
  • Predominant race: all races
Precise pathophysiology is uncertain. Circulating antigens may react with antibodies at sensitized areas of the skin. An abnormal immune recognition of autologous skin antigens may also occur. Inflammation may lower the irritation threshold of the skin, and hematogenous spread of cytokines from the primary site of inflammation may also play a role (1).
  • Etiology
    • Infectious
      • Fungal infections: Trichophyton mentagrophytes, Trichophyton rubrum, Epidermophyton floccosum, and Candida spp.
      • Bacterial infections: Streptococcus pyogenes, Staphylococcus aureus, and Mycobacterium tuberculosis
      • Viral infections: HSV, Molluscum contagiosum, orf, and milker's nodules
      • Parasitic infections: Sarcoptes scabiei and Leishmania spp.
    • Allergic
      • Id reactions occur in patients with nickel and aluminum allergy.
    • Miscellaneous
      • Id reaction rarely develop due to retained postoperative sutures, ionizing radiation, and blunt trauma.
      • Rarely, id reaction has been documented in patients receiving intravesical BCG live therapy for transitional cell carcinoma.
  • Fungal infection of the skin, especially tinea pedis
  • Stasis dermatitis
  • Good skin hygiene (particularly in intertriginous areas) to minimize risk of developing fungal infections
  • Promptly treat any developing fungal infection.
  • Primary fungal infection
  • Stasis dermatitis
  • Common
    • Symmetric, pruritic vesicles on the palms and, most commonly, on lateral aspects of fingers
    • Tinea infection on the feet; contact or other eczematous dermatosis; bacterial, fungal, or viral infection of the skin
  • Less common
    • Papules
    • Lichenoid eruption
  • Eczematoid eruption
  • Pompholyx (dyshidrotic eczema)
  • Contact dermatitis
  • Drug eruptions
  • Pustular psoriasis
  • Folliculitis
  • Scabies
  • Potassium hydroxide (KOH) or fungal culture of primary lesion
  • No fungal elements are present at the site of the id reaction.
  • Special tests: Skin shows a positive trichophyton reaction. A wheal >10 mm at 20 minutes and induration >5 mm at 72 hours is a positive response.
Follow-Up Tests & Special Considerations
  • The id reaction resolves with successful eradication of the primary skin condition.
  • It is important to distinguish dermatophytids from drug-induced allergic reactions, as continued treatment is essential to clear the underlying infection.
Test Interpretation
  • Vesicles in the upper dermis
  • Superficial perivascular lymphohistiocytic infiltrate with small numbers of eosinophils and increased granular cell layer
  • No infectious agents present in biopsy specimen
  • Outpatient treatment of the underlying infection or eczematous dermatitis
  • Symptomatic treatment of pruritus with antihistamines and/or topical steroids if needed (may require class 1 or 2 steroid)
  • Treatment for secondary bacterial infection

First Line
  • PO antihistamines for pruritus (2)
    • Chlorpheniramine: 4 mg PO q4-6h PRN; max 24 mg/24 hr; (pediatric: 6 to 11 years 2 mg PO q4-6h PRN; max 12 mg/24 hr; ≥12 years, refer to adult dosing)
    • Diphenhydramine: 25 to 50 mg PO q4-6h PRN; max 400 mg/24 hr; (pediatric: 5 mg/kg/24 hr divided q6h PRN; 2 to 5 years max 37.5 mg/24 hr; 6 to 11 years max 150 mg/24 hr; ≥12 years, refer to adult dosing)
    • Hydroxyzine: 25 to 100 mg PO q6-8h PRN; max 600 mg/24 hr; (pediatric: 2 mg/kg/24 hr divided q6h PRN)
  • Topical treatments for pruritus
    • Triamcinolone 0.1% ointment TID
    • Hydrocortisone 0.5%, 1%, 2.5%: up to QID
    • Capsaicin 0.025%, 0.075% cream: Apply TID-QID; EMLA (2.5% lidocaine + 2.5% prilocaine) applied 30 to 60 minutes prior to capsaicin may minimize burning.
    • Doxepin 5% cream: Apply QID for up to 8 days (to max of 10% of the body).
    • Permethrin 5% cream (for scabies)
      • Apply from neck down after bath.
      • Wash off thoroughly with water in 8 to 12 hours.
      • May repeat in 7 days
    • Permethrin 1% cream rinse (for lice)
      • Shampoo, rinse, towel dry, saturate hair and scalp (or other affected area), leave on 10 minutes, then rinse.
      • May repeat in 7 days
    • White petroleum emollients: Apply after short bath/shower in warm (not hot) water.
  • Systemic steroids only if reaction is severe or generalized (e.g., prednisone 20 mg)
Second Line
  • Topical and/or systemic antifungals for identified associated fungal infection (common)
    • Tinea cruris/corporis
      • Topical azole antifungal compounds econazole (Spectazole) and ketoconazole (Nizoral): usually applied BID for 2 to 4 weeks
      • Terbinafine (Lamisil): over-the-counter (OTC) compound; can be applied daily or BID for 1 to 2 weeks
      • Butenafine (Mentax): applied once daily for 2 weeks; also very effective
    • Tinea capitis
      • PO griseofulvin for Trichophyton and Microsporum sp.; microsized preparation available; dosage 20 to 25 mg/kg/day divided BID or as a single dose daily for 6 to 12 weeks
      • PO terbinafine can be used for Trichophyton sp. at 62.5 mg/day in patients weighing 10 to 20 kg, 125 mg/day if weight 20 to 40 kg, 250 mg/day if weight >40 kg, and use for 4 to 6 weeks.
  • Topical or systemic antibiotics for any secondary bacterial infection
  • Treatment with antiviral agents for erythema multiforme associated with HSV is required.
Avoid hot, humid conditions that promote fungal growth. Aerate susceptible body areas (e.g., wear sandals or open footwear). If possible, wear loosefitting clothing and undergarments, dry wet skin after bathing, and use powders and antiperspirants to discourage fungal growth. Treat primary dermatitis promptly.
After appropriate treatment, complete resolution in days to weeks
1. Ilkit M, Durdu M, Karakaş M. Cutaneous id reactions: a comprehensive review of clinical manifestations, epidemiology, etiology, and management. Crit Rev Microbiol. 2012;38(3):191-202.
2. Cotes ME, Swerlick RA. Practical guidelines for the use of steroid-sparing agents in the treatment of chronic pruritus. Dermatol Ther. 2013;26(2):120-134.
Additional Reading
  • Elmariah SB, Lerner EA. Topical therapies for pruritus. Semin Cutan Med Surg. 2011;30(2):118-126.
  • Paulsen LL, Geller DD, Guggenbiller M. Symmetrical vesicular eruption on the palms. Am Fam Physician. 2012;85(8):811-812.
  • Stachler RJ, Al-khudari S. Differential diagnosis in allergy. Otolaryngol Clin North Am. 2011;44(3): 561-590, vii-viii.
  • Veien NK. Acute and recurrent vesicular hand dermatitis. Dermatol Clin. 2009;27(3):337-353, vii.
  • Yosipovitch G, Bernhard JD. Clinical practice. Chronic pruritus. N Engl J Med. 2013;368(17):1625-1634.
  • L30.2 Cutaneous autosensitization
  • B35.9 Dermatophytosis, unspecified
Clinical Pearls
  • When one skin eruption follows another closely in time, consider an id reaction.
  • When assessing an itchy rash, inquire about potential fungal or bacterial lesions in the preceding days to weeks as a potential prelude to the id reaction.