What is the appropriate management for phytophotodermatitis presenting as a localized burn‑like rash after handling photosensitizing plants and sun exposure?

Management of Phytophotodermatitis

For phytophotodermatitis presenting as a localized burn-like rash after plant contact and sun exposure, immediately discontinue further sun exposure, apply potent topical corticosteroids to affected areas, and provide systemic corticosteroids (prednisolone 20-40 mg daily) for severe inflammation with blistering. 1

Immediate Management Algorithm

Acute Phase Treatment (First 24-72 Hours)

• Mild reactions (localized erythema without blistering, <10% body surface area): Apply high-potency topical corticosteroids to affected areas twice daily and use emollients for symptomatic relief 1, 2

• Moderate reactions (vesicles/bullae present, 10-30% body surface area, or limiting daily activities): Initiate oral prednisolone 0.5-1 mg/kg daily tapered over 4 weeks, combined with medium-to-high potency topical corticosteroids 1, 2

• Severe reactions (extensive blistering, >30% body surface area, or systemic symptoms): Start prednisolone 1 mg/kg/day tapered over at least 4 weeks, consider dermatology consultation, and provide wound care for bullae 2, 3

• Complete sun avoidance is mandatory until the acute reaction resolves, as continued UV exposure will worsen the phototoxic injury 1

Supportive Care Measures

• Provide analgesia as needed for the burning pain that characteristically develops within 24 hours of exposure 4, 3

• Maintain wound hygiene for any blistered areas to prevent secondary infection 4

• Educate patients that hyperpigmentation will develop in affected areas as the acute inflammation resolves, typically lasting weeks to months 5, 6

Diagnostic Confirmation

The diagnosis is primarily clinical, based on three key features:

• Sharp demarcation of the rash corresponding exactly to areas of plant contact (e.g., handprints, drip patterns, or areas not covered by clothing) 3, 6

• Temporal sequence: Burning sensation and erythema developing within 24 hours of combined plant contact and sun exposure, progressing to vesicles/bullae, then hyperpigmentation 3, 6

• History of exposure to high-risk plants from the Apiaceae family (celery, parsnips, cow parsnip), Rutaceae family (citrus fruits including limes), or Moraceae family (fig trees) 1, 5, 4

Diagnostic Testing When Needed

• Wood's lamp examination can reveal hyperpigmentation patterns in resolved cases 5

• Skin biopsy (if diagnosis uncertain) shows sub-epithelial blisters with intensive epidermal necrosis, distinguishing it from allergic contact dermatitis 3

• Patch testing is generally not indicated, as phytophotodermatitis is a phototoxic (not allergic) reaction 5

Common Diagnostic Pitfalls to Avoid

Phytophotodermatitis is frequently misdiagnosed as:

• Cellulitis: The erythema and edema can mimic infection, but the sharp geometric borders and absence of fever/systemic symptoms distinguish phytophotodermatitis 3, 7

• Allergic contact dermatitis: Unlike type IV hypersensitivity, phytophotodermatitis requires both plant contact AND UV exposure, and has characteristic linear or splash patterns 7, 6

• Second-degree burns: The vesicles and bullae appear burn-like, but the history of plant exposure and bizarre geometric patterns are diagnostic clues 4, 6

• Child abuse: In pediatric cases, the unusual distribution may raise concern, making accurate history-taking essential 7

Prevention Strategies for Future Exposure

Primary Prevention

• Avoid contact with psoralen-containing plants (citrus, celery, fig trees, parsnips, cow parsnip) for at least 2 hours before sun exposure 1

• When handling potentially phototoxic plants, wear long-sleeved garments, long pants, and gloves to prevent skin contact 1, 5

• If plant contact occurs, immediately wash the affected area thoroughly with soap and water before any sun exposure 4

Photoprotection Measures

• Apply broad-spectrum sunscreen with SPF ≥30 to all exposed skin areas, with particular attention to hands and forearms when handling plants 1

• Reapply sunscreen every 2 hours and after water exposure 1

• Avoid peak UV hours (10 AM to 4 PM) when working with or around high-risk plants 1, 2

Long-Term Monitoring Considerations

• For patients with history of severe phytophotodermatitis, annual full-body skin examinations by a dermatologist are recommended to monitor for any long-term sequelae 1

• Patient education on self-examination for new or changing lesions in previously affected areas 1

• The hyperpigmentation phase is asymptomatic but can persist for months; reassure patients this will gradually fade without additional treatment 5, 6