Pathophysiology
- ICD: Direct cytotoxic damage to keratinocytes. No immune sensitization required. Occurs on first exposure if irritant is strong enough
- ACD: Type IV (delayed) hypersensitivity reaction. Requires prior sensitization (first exposure sensitizes T-cells; subsequent exposures trigger inflammation within 24-72 hours)
- Both types cause inflammatory mediator release, vasodilation, increased vascular permeability, and edema
- Chronic exposure leads to lichenification (thickened, leathery skin)
- Common allergens: nickel, latex, fragrances, preservatives, poison ivy/oak
- Common irritants: soaps, detergents, solvents, acids, alkalis
Signs and Symptoms
Hallmark Indicators
- Acute: Erythema (redness), pruritus (itching), edema, vesicles, weeping at the contact site
- Subacute: Crusting, scaling, mild erythema
- Chronic: Lichenification, fissuring, dry thickened skin
- Distribution pattern matches the area of contact (e.g., wristwatch = wrist; massage oil = therapist's hands)
- ACD has sharply demarcated borders corresponding to exposure area
- Secondary bacterial infection possible if barrier broken by scratching
Red Flags and Rule-Outs
- Widespread, non-contact-pattern rash: Suggests systemic reaction rather than contact dermatitis
- Acute weeping vesicles: Local contraindication — do not massage the area
- Distinguish ICD (no sensitization needed) from ACD (Type IV delayed, requires prior exposure)
- Patch test (medical referral): Standard for identifying the specific allergen in ACD
MT Considerations
- Prevention is paramount: Always ask about known skin allergies and sensitivities before selecting lubricants
- Lubricant patch test: Apply a small amount to unaffected skin (inner forearm) and wait 30 minutes before full application
- Local contraindication: Active weeping, vesicular, or acutely inflamed dermatitis — avoid the area
- Chronic phase: Dry, lichenified patches may tolerate gentle massage with hypoallergenic lubricant
- Therapist self-care: RMTs with hand dermatitis should use barrier creams, moisturize, and consider nitrile gloves
- Default products: Unscented, hypoallergenic, fragrance-free lubricants for all clients with sensitive skin
- Not contagious: Inflammatory reaction, not an infection
CMTO Exam Relevance
- Distinguish ICD (direct damage, no sensitization) from ACD (Type IV delayed, requires prior sensitization)
- Distribution pattern matching the contact area is the key diagnostic clue
- Massage lubricants, essential oils, and latex gloves are common triggers
- Acute weeping vesicles are a local contraindication. Chronic dry patches are a precaution
- Patch test is the medical standard for identifying the specific allergen
Key Takeaways
- Contact dermatitis is an inflammatory reaction from irritant or allergen exposure, not an infection
- ICD is direct chemical damage. ACD is a Type IV delayed hypersensitivity requiring prior sensitization
- Distribution pattern matching the contact area is the hallmark diagnostic feature
- Always perform a lubricant patch test for new clients or new products
- Active weeping lesions are locally contraindicated. Chronic dry patches are a precaution