What are the differential diagnoses for a middle-aged female presenting with dermatitis of the lower face after exposure to questionable water while sifting for gold and bathing in a rural or wilderness setting?

Differential Diagnoses for Lower Face Dermatitis Following Water Exposure

Primary Differential Diagnoses to Consider

The most critical diagnoses to evaluate in this patient are irritant contact dermatitis from contaminated water exposure, allergic contact dermatitis to metals or chemicals in the water (particularly gold-related compounds), bacterial folliculitis from water-borne organisms, and less commonly, photocontact dermatitis if sun exposure occurred during the activity. 1, 2

Irritant Contact Dermatitis (ICD)

• ICD is the most common form of contact dermatitis and represents the cutaneous response to toxic/physical effects of environmental agents, making it a primary consideration given prolonged water exposure 2
• The pathophysiology involves skin barrier disruption, cellular changes, and release of proinflammatory mediators through activation of the innate immune system 2
• Clinical presentation varies based on irritant properties, dose, duration and frequency of exposure, and individual skin susceptibility 2
• Water itself acts as an irritant, particularly with prolonged exposure, and contaminated water may contain multiple chemical and biological irritants 3, 2
• The lower face distribution is consistent with direct contact during bathing and potential splash exposure during gold sifting 3

Allergic Contact Dermatitis (ACD)

• ACD should be strongly considered given the exposure to questionable water that may contain metals, chemicals, or organic compounds from gold mining activities 3, 1
• This represents a type IV delayed hypersensitivity reaction to small environmental chemicals (haptens) that bind to epidermal carrier proteins 3
• The most common contact allergens include nickel, formaldehyde and other preservatives, which could be present in contaminated mining water 3
• Facial and lower face involvement is a classic pattern suggesting aeroallergen or direct contact exposure 3
• Diagnosis requires patch testing on unaffected skin, typically the back, with readings at 48 hours and up to 7 days for delayed reactions 3

Bacterial Folliculitis

• Water-borne bacterial organisms, particularly Staphylococcus aureus and Pseudomonas aeruginosa (hot tub folliculitis), commonly cause folliculitis after contaminated water exposure 4
• Look for discrete pustules centered on hair follicles, particularly in areas of occlusion and sweating 4
• Secondary bacterial infection may complicate underlying dermatitis, presenting with crusting, weeping, or increased erythema 3, 5
• Oral antibiotics such as flucloxacillin for Staphylococcus aureus or appropriate coverage for Pseudomonas may be indicated if bacterial infection is evident 4, 5

Photocontact Dermatitis

• Photocontact dermatitis results from simultaneous exposure to a contactant and ultraviolet light, which is highly relevant if the patient had sun exposure during outdoor gold sifting 6
• Can be subdivided into photoallergic and photoirritant types depending on the mechanism 6
• Photoirritant reactions are commonly caused by plants, psoralens, and certain chemicals that may be present in natural water sources 6
• Distribution typically affects sun-exposed areas including the face, neck, arms, and "V" area of the chest 3, 6

Water-Related Dermatoses

• Direct water exposure can cause specific dermatoses including aquagenic reactions, though these are less common than irritant or allergic contact dermatitis 7
• Freshwater and marine organisms can cause cutaneous injuries requiring distinct identification and management 7
• Consider parasitic infections if the water source was in an endemic area, though these typically present differently than simple dermatitis 7

Critical Diagnostic Distinctions

Exclude Infectious Etiologies

• Look for grouped, punched-out erosions suggesting herpes simplex superinfection, which requires immediate treatment with oral acyclovir 5
• Examine for burrows, inguinal/genital involvement, and palmoplantar vesicles to exclude scabies 4
• Consider fungal infections, though these typically have different morphology with well-demarcated borders and central clearing 5

Distinguish from Other Eczematous Conditions

• Atopic dermatitis typically presents with more intense pruritus, lichenification in chronic cases, and flexural involvement rather than isolated lower face distribution 3, 5
• Seborrheic dermatitis shows greasy, yellow scales in seborrheic areas (nasolabial folds, eyebrows) rather than the pattern expected from water contact 5
• Psoriasis presents with well-demarcated, indurated plaques with thick silvery scale, not the acute eczematous changes expected from recent water exposure 5

Diagnostic Approach Algorithm

Initial Clinical Assessment

• Document the exact distribution pattern—sharp demarcation corresponding to water contact areas strongly suggests contact dermatitis 3, 5
• Assess for oozing, crusting, and discrete pustules versus less discrete inflammatory changes 4
• Examine for follicular-centered lesions suggesting folliculitis versus more diffuse eczematous changes 4

Patch Testing Indications

• Patch testing should be performed when history and physical exam suggest ACD, particularly with facial involvement, unusual distribution, or recalcitrant disease not responding to standard therapies 3
• Testing requires skin free from active dermatitis and should be delayed if patient is on systemic corticosteroids >10mg prednisolone daily 3
• Avoid testing within 2 days of potent topical steroid application to the back to prevent false negatives 3

Laboratory and Culture Considerations

• Bacterial culture and sensitivity if folliculitis or secondary infection is suspected, looking for Staphylococcus aureus or Pseudomonas species 4, 5
• Consider fungal culture if tinea is in the differential, though clinical presentation usually differs 5

Common Pitfalls to Avoid

• Do not assume all facial dermatitis is seborrheic dermatitis or atopic dermatitis without considering the temporal relationship to water exposure 3, 1
• Avoid dismissing contact dermatitis because the patient has no prior history—sensitization can occur at any age, and this represents a novel exposure 3, 1
• Do not overlook the possibility of multiple concurrent conditions—irritant dermatitis, allergic contact dermatitis, and bacterial folliculitis may coexist 3, 8
• Recognize that "questionable water" in gold mining areas may contain heavy metals (mercury, arsenic), industrial chemicals, and biological contaminants that can cause both irritant and allergic reactions 1, 2
• Avoid patch testing during active flares or on inflamed skin, as this increases risk of false positives ("angry back syndrome") 3