Plants That Cause Phytophotodermatitis
The primary plant families causing phytophotodermatitis are Apiaceae (celery, parsnips, parsley, giant hogweed), Rutaceae (citrus fruits, especially limes), and Moraceae (fig trees), all containing furanocoumarins (psoralens) that become phototoxic upon UV light exposure. 1, 2
High-Risk Plant Families and Species
Apiaceae Family (Umbelliferae)
The Apiaceae family represents the highest-risk group for phytophotodermatitis 1:
- Giant hogweed (Heracleum mantegazzianum) - causes severe burn-like reactions with extensive bullae formation 2, 3, 4
- Wild parsnip (Pastinaca sativa) - increasingly found on roadsides and prairies in North America, with stems and leaves containing high furanocoumarin concentrations 2, 5, 4
- Celery (Apium graveolens) - common culprit in food handlers and during PUVA therapy 6, 1, 2
- Parsley (Apium petroselinum) - documented to cause partial-thickness burns when combined with sun exposure 4
Rutaceae Family
- Citrus fruits (limes, lemons, oranges) - lime-induced photodermatitis is particularly well-documented, with furocoumarin content being the key phototoxic agent 1, 2
- Rue (Ruta graveolens) - contains significant psoralen compounds 2
Moraceae Family
- Fig trees (Ficus carica) - both the fruit and leaves contain photosensitizing compounds; multiple cases reported from patients soaking feet in fig leaf decoctions 2, 7
Mechanism of Phototoxicity
All these plants contain furanocoumarins (psoralens) that require sequential exposure: first contact with the plant material, then exposure to ultraviolet A (UVA) radiation 2, 7, 5. Upon UVA activation, these compounds interact with oxygen to generate reactive oxygen species that directly damage DNA and cellular structures, causing erythema, edema, vesicles, bullae, and subsequent hyperpigmentation 2, 5.
Clinical Recognition Pitfalls
Phytophotodermatitis is frequently misdiagnosed as cellulitis, tinea, or allergic contact dermatitis 7. Key distinguishing features include:
- Sharply demarcated borders corresponding to areas of plant contact and sun exposure 7
- Sparing of covered areas (e.g., skin under sandal straps) 7
- Delayed onset of burning sensation and erythema within 24 hours of exposure 7
- Linear or bizarre patterns reflecting the distribution of plant sap on skin 2
Critical Timing for Prevention
Avoid contact with psoralen-containing plants for at least 2 hours before any sun exposure, as recommended for patients undergoing PUVA therapy, where enhancement of phototoxicity has been documented after ingestion of celery and vegetable broths 6, 1.