Why is phototherapy contraindicated in patients with porphyria?

Why Porphyria is a Contraindication to Phototherapy

Phototherapy is absolutely contraindicated in patients with porphyria because the light exposure activates accumulated porphyrins in the skin, generating reactive oxygen species that cause severe phototoxic reactions including painful burning, blistering, bullous eruptions, and permanent tissue damage. 1

Pathophysiologic Mechanism

The fundamental problem in porphyria is the accumulation of porphyrins—fluorescent chemicals that become photoactivated when exposed to light in the 400-410 nm wavelength range (which includes the blue-green spectrum used in phototherapy). 1, 2

Direct Cellular Damage Pathway

• Porphyrins absorb light energy and transfer it to oxygen molecules, creating singlet oxygen and other reactive oxygen species (ROS) that directly damage cell membranes, proteins, and surrounding tissues. 2, 3
• These ROS activate pain receptors (TRPA1 and TRPV1 channels) in sensory neurons, causing the characteristic severe burning pain that porphyria patients experience with light exposure. 2
• The phototoxic reaction leads to immediate erythema, edema, and in severe cases, bullous eruptions with bloody fluid accumulation covering all light-exposed skin surfaces. 3, 4

Inflammatory Cascade

• Photoactivated porphyrins trigger complement system activation, which in turn activates dermal mast cells to release proteases and inflammatory mediators. 3
• This cascade results in dermal-epidermal separation (causing skin fragility and vesicles), direct membrane damage to fibroblasts, and chronic fibrosis leading to sclerodermoid changes. 3

Clinical Consequences of Phototherapy in Porphyria

Acute Severe Reactions

• A documented case of a newborn with congenital erythropoietic porphyria who received phototherapy for jaundice developed severe bullous dermatosis after only 18 hours of light exposure, with bloody blistering covering all exposed body surfaces that recurred in multiple episodes despite light protection, ultimately contributing to the infant's death. 4
• The severity of phototoxic reactions in porphyria far exceeds normal phototherapy side effects—patients develop not just erythema but actual tissue destruction with blistering and permanent scarring. 3, 4

Chronic Tissue Damage

• Repeated or prolonged light exposure in porphyria patients causes waxy thickening of skin, hyperpigmentation, hypertrichosis, and fragmentation of dermal collagen bundles. 3, 5

Specific Guideline Recommendations

Absolute Contraindications Across All Phototherapy Types

• The American Academy of Dermatology explicitly lists porphyria as an absolute contraindication to both UVB phototherapy and PUVA (psoralen plus UVA) photochemotherapy. 1
• The British Association of Dermatologists similarly identifies porphyria as a contraindication to topical PUVA and photodynamic therapy. 1
• For neonatal phototherapy, the American Academy of Pediatrics states that congenital porphyria or family history of porphyria represents an absolute contraindication. 1, 6

Critical Distinction from Bronze Baby Syndrome

• Bronze baby syndrome (dark skin discoloration in infants with cholestasis receiving phototherapy) is NOT a contraindication to continuing phototherapy if clinically needed, whereas congenital erythropoietic porphyria presenting with severe blistering and bullous eruptions IS an absolute contraindication. 6
• The key distinguishing feature is that porphyria causes severe bullous eruptions and tissue destruction, not just pigmentation changes. 6, 4

Practical Clinical Algorithm

Before Initiating Any Phototherapy

1. Screen all patients for personal or family history of porphyria, photosensitivity disorders, or unexplained blistering with sun exposure. 1
2. If any suspicion exists, measure plasma fluorescence scanning (first-line test) and urine/fecal porphyrin fractionation before proceeding. 1
3. In neonates, if severe bullous eruptions or purpura develop during phototherapy, immediately discontinue treatment and test for congenital erythropoietic porphyria. 6, 4

If Porphyria is Diagnosed

• Absolutely do not initiate or continue phototherapy of any type (UVB, PUVA, photodynamic therapy, or neonatal blue light). 1
• Implement strict visible light photoprotection measures, as even ambient light can trigger reactions in severe cases. 7

Common Pitfall to Avoid

The rarity of porphyria (particularly congenital erythropoietic porphyria) does not justify ignoring it as a contraindication—while one case report suggested it's too rare to be a "general contraindication," the severity of reactions when they occur makes screening essential. 4 The documented fatality in the neonatal case underscores that even rare contraindications must be respected in clinical practice. 4