Contact Dermatitis

Table of Contents

1. Two Types of Contact Dermatitis
2. Irritant Contact Dermatitis Causes
3. Allergic Contact Dermatitis: Common Allergens
4. Clinical Presentation
5. Patch Testing
6. Acute Treatment
7. Avoidance Strategies
8. Occupational Contact Dermatitis
9. Research Papers
10. Connections
11. Featured Videos

Two Types of Contact Dermatitis

Contact dermatitis is skin inflammation caused by direct skin contact with a substance. There are two completely different mechanisms — understanding which type you have is essential for treatment:

• Irritant Contact Dermatitis (ICD) — 80% of cases: A non-immune reaction in which the substance directly damages the skin barrier. Anyone's skin will eventually react to enough exposure to a strong enough irritant. No prior sensitization is required — it is not an allergy. Common example: dishpan hands from repeated soap and water exposure.
• Allergic Contact Dermatitis (ACD) — 20% of cases: A Type IV delayed hypersensitivity reaction mediated by T lymphocytes. Only people who have been previously sensitized to a specific allergen react. The first exposure causes sensitization (no rash); subsequent exposures trigger the allergic cascade. Classic example: poison ivy rash.

Both types cause a similar-looking rash, but the history, timing, and treatment approach differ significantly. ICD occurs immediately to hours after exposure; ACD occurs 12–72 hours after re-exposure in a sensitized individual.

Irritant Contact Dermatitis Causes

ICD results from repeated barrier damage. The skin can only repair itself so fast — constant irritant exposure outpaces recovery:

• Wet work: The single most important cause of occupational ICD. Repeated hand washing, immersion in water, or wearing occlusive gloves for extended periods. Healthcare workers, nurses, hairdressers, dishwashers, food processors, and bartenders are at highest risk.
• Soaps and detergents: Strip the skin's lipid barrier. Concentrated or industrial-strength products cause more rapid damage than household products.
• Acids and alkalis: Strong chemicals cause immediate burns and irritation. Even mild acids (vinegar, citrus) can cause ICD with repeated exposure.
• Solvents: Acetone, gasoline, turpentine, and other organic solvents dissolve skin lipids.
• Friction: Mechanical rubbing — tools, ill-fitting shoes, tight clothing — causes calluses and skin breakdown.
• Diaper rash: The most common form of ICD in infants. Urine and feces in prolonged contact with skin — ammonia from bacterial breakdown of urine is particularly irritating. Superimposed Candida infection is extremely common and changes the treatment.

Allergic Contact Dermatitis: Common Allergens

Thousands of substances can cause ACD. These are the most clinically important:

• Nickel: The most common contact allergen worldwide, particularly in women (due to jewelry exposure). Found in earrings, belt buckles, jean buttons, watchbands, bra clasps. The earring rule: if cheap earrings cause itchy red ears within 24–48 hours, you likely have nickel allergy — switch to surgical steel, titanium, or 18K+ gold.
• Urushiol (poison ivy, oak, sumac): The most intense plant-based allergen. Even minute amounts (nanograms) can trigger severe blistering dermatitis in sensitized individuals. Urushiol can remain active on surfaces, tools, and clothing for years. Smoke from burning poison ivy can cause lung injury.
• Fragrances: The most common cosmetic allergen. "Fragrance" on an ingredient list can represent any of thousands of compounds. Look for fragrance-free (not "unscented" — which may contain masking fragrances). Common culprits include Balsam of Peru, cinnamal, and geraniol.
• Preservatives: Methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI/MI) — widely used in rinse-off and leave-on cosmetic products — are now among the most common contact allergens in Europe. Formaldehyde-releasing preservatives (imidazolidinyl urea, diazolidinyl urea, DMDM hydantoin) are also common.
• Rubber chemicals: Thiurams, carbamates, and mercaptobenzothiazole (MBT) in latex gloves, shoe soles, elastic waistbands. Thiuram is the most common rubber allergen. Latex protein allergy (Type I immediate hypersensitivity) is different and more dangerous.
• Para-phenylenediamine (PPD): Found in permanent hair dye, black henna tattoos, and some rubber products. Hair dye ACD typically presents as blistering dermatitis at the hairline, ears, and neck.
• Chromate (potassium dichromate): Found in cement, leather, and some paints. A major cause of hand dermatitis in construction workers.
• Formaldehyde: Found in nail polish (as a hardener), "permanent press" fabric finishes, and some personal care products. "Formaldehyde-free" nail polishes are available.

Clinical Presentation

The rash distribution is your biggest diagnostic clue — it often outlines the exact area of contact:

• Irritant Contact Dermatitis: Redness, dryness, scaling, fissures (cracks), and burning or stinging that begins during or shortly after contact. The rash is sharply confined to the area of exposure. Chronic ICD shows thickening (lichenification), scaling, and fissuring without much oozing.
• Allergic Contact Dermatitis: Intensely itchy rash appearing 12–72 hours after re-exposure. Features include redness, swelling, papules (bumps), vesicles (tiny fluid-filled blisters), and weeping. The rash may spread beyond the direct contact area because allergen-specific T cells circulate systemically. Severe cases (like poison ivy) can cause dramatic swelling, especially around the eyes.

Pattern recognition helps identify the allergen:

• Earlobe rash → nickel in earrings
• Wrist rash → nickel watch buckle or watchband rubber
• Waistband rash → nickel in jeans button or rubber elastic
• Scalp/hairline rash → hair dye (PPD)
• Foot rash matching shoe sole → rubber or chromate in footwear
• Linear streaks on arms → poison ivy brushed against skin

Patch Testing

Patch testing is the gold standard for diagnosing ACD. It identifies which specific allergen is responsible — critical information for long-term avoidance. It is NOT the same as a scratch test (which tests for IgE-mediated Type I allergy like bee sting or food allergy).

• T.R.U.E. Test (Thin-Layer Rapid Use Epicutaneous Test): FDA-cleared panels of 36 common allergens applied to the back. Widely available in dermatology offices. Sufficient for diagnosing 80% of common contact allergies.
• Extended patch testing: For patients who test negative on standard panels but have strong clinical suspicion, extended series of 80+ allergens can be tested. Requires specialized contact dermatitis clinics.
• How it works: Patches are applied to the upper back for 48 hours, then read at 48 hours and again at 96 hours (or Day 7). A positive reaction shows a localized eczematous response exactly where the allergen patch was placed. Must distinguish true allergy (growing reaction at 96h) from irritant reactions (fading at 96h).
• Preparation: Avoid topical steroids or immunosuppressants on the back for 2 weeks before testing, as these can suppress reactions and cause false negatives.

Acute Treatment

The first step is always remove the source — wash the skin thoroughly with soap and water, remove contaminated clothing, and identify and eliminate the offending substance. Then:

• Topical corticosteroids: The mainstay of treatment. Use moderate to high potency on the body (triamcinolone 0.1%, fluocinonide 0.05%); low potency on the face (hydrocortisone 1%). Apply twice daily for 1–2 weeks. Do not use high-potency steroids on the face, groin, or armpits long-term.
• Wet compresses: Cool, moist dressings applied to weeping/blistering areas for 15–30 minutes several times daily. Burow's solution (aluminum acetate) has mild astringent and antimicrobial properties. Wet compresses reduce oozing and provide soothing relief.
• Oral antihistamines: Diphenhydramine (Benadryl) or hydroxyzine helps with itching and improves sleep during acute flares. Newer non-sedating antihistamines (cetirizine, loratadine) have less proven benefit for contact dermatitis-associated itch.
• Systemic corticosteroids (for severe ACD — especially poison ivy): Oral prednisone 0.5–1 mg/kg/day for 7–10 days minimum (must taper gradually — abrupt discontinuation after 5 days causes rebound). A common mistake is prescribing only a 5-day "dose pack" (Medrol pack) — this is insufficient for poison ivy and causes rebound flare when stopped.
• Calamine lotion: Drying, anti-itch topical for mild poison ivy rash. Effective for oozing stages but may worsen dry/scaling phases.

Avoidance Strategies

Once the allergen is identified through patch testing, long-term avoidance is the cure for ACD:

• Nickel allergy: Switch to surgical steel, titanium, niobium, or 18K+ gold jewelry. Apply nail polish to the inside of belt buckles and buttons to create a barrier. Nickel barrier creams (containing chelating agents) are available but less reliable than substitution.
• Latex allergy: Switch to nitrile or vinyl gloves. Inform all healthcare providers before procedures — latex in surgical gloves and medical equipment poses serious risk (anaphylaxis in severe cases).
• Fragrance allergy: Use fragrance-free products for all personal care (shampoo, conditioner, moisturizer, soap, deodorant). Many "natural" products still contain high fragrance loads — essential oils are potent allergens.
• Hair dye allergy (PPD): Switch to henna without PPD, gradual darkening shampoos, or semi-permanent dyes free of PPD. Always patch test new dyes behind the ear 48 hours before full application.
• Wet work/ICD prevention: Barrier creams (dimethicone, petrolatum-based) applied before work; cotton glove liners under rubber gloves to absorb sweat; limiting wet work to under 2 hours/day when possible; aggressive skin barrier repair with emollients after work.
• Poison ivy: Learn to identify the plant ("leaves of three, let it be"). Wear long sleeves and gloves when outdoors in affected areas. Barrier creams containing bentoquatam (IvyBlock) provide partial protection if applied before exposure. Wash exposed skin within 10 minutes of contact to reduce severity.

Occupational Contact Dermatitis

Occupational contact dermatitis accounts for 15–20% of all occupational disease cases and is one of the most common reasons for workers' compensation claims. It disproportionately affects healthcare workers, hairdressers, cosmetologists, construction workers, cleaners, food processors, and mechanics.

Key principles for management:

• Early identification and patch testing are critical — chronic sensitized skin becomes more reactive over time, and continuing exposure despite sensitization worsens outcomes significantly
• Workplace modification (substitution of less irritating chemicals, improved ventilation, automation to reduce skin contact) is often more effective than individual protective equipment alone
• Occupational dermatitis may qualify for workers' compensation and may necessitate job reassignment if allergen avoidance is not possible in the current role
• Hairdressers with glyceryl thioglycolate allergy (perm solutions) or PPD allergy (hair dye) may be unable to continue working in their profession

Research Papers

Key peer-reviewed studies on contact dermatitis mechanisms, patch testing, and treatment. Each PMID link opens the study on PubMed.

1. Fonacier L, Bernstein DI, Pacheco K, et al. Contact dermatitis: a practice parameter-update 2015. J Allergy Clin Immunol Pract. 2015;3(3 Suppl):S1-39. — Search PubMed
2. Nosbaum A, et al. Contact dermatitis. Eur J Dermatol. 2009;19(4):325-332. — Search PubMed
3. Borda LJ, Wikramanayake TC. Seborrheic dermatitis and dandruff: a comprehensive review. J Clin Investig Dermatol. 2015;3(2). — Search PubMed
4. Borda LJ, Wikramanayake TC. Seborrheic dermatitis and dandruff. J Clin Investig Dermatol. 2015. — Search PubMed
5. Gupta AK, Bluhm R. Seborrheic dermatitis. J Eur Acad Dermatol Venereol. 2004. — Search PubMed
6. Zug KA, et al. Patch-test results of the North American Contact Dermatitis Group 2005-2006. Dermatitis. 2009;20(3):149-160. — Search PubMed
7. Gupta AK, Madzia SE, Batra R. Etiology and management of seborrheic dermatitis. Dermatology. 2004. — Search PubMed
8. Naldi L, Rebora A. Clinical practice: seborrheic dermatitis. N Engl J Med. 2009. — Search PubMed
9. Saary J, et al. A systematic review of contact dermatitis treatment and prevention. J Am Acad Dermatol. 2005;53(5):845-855. — Search PubMed
10. Ale IS, Maibach HI. Irritant contact dermatitis. Rev Environ Health. 2014;29(3):195-206. — Search PubMed

Curated PubMed topic searches:

1. PubMed: Patch testing
2. PubMed: Nickel contact allergy
3. PubMed: Urushiol/poison ivy
4. PubMed: Occupational ICD
5. PubMed: Fragrance allergy
6. PubMed: Latex allergy
7. PubMed: Corticosteroid treatment
8. PubMed: PPD hair dye allergy

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Connections

• Eczema
• Psoriasis
• Rosacea
• Seborrheic Dermatitis
• Hidradenitis Suppurativa
• Allergies
• Latex Allergy
• Chamomile
• Zinc
• Vitamin D3
• Elimination Diet

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