[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Skin](https://durgical.com/en/general-pathology/areas/skin/) › Epidermolysis bullosa and porphyria

# Epidermolysis bullosa and porphyria

- Lesion

Some blisters come from inherited weak skin proteins or from light-sensitive pigments, not from inflammation.

Updated Nov 12, 2026

## Key points

- EB simplex: keratin 5 or 14 mutations; basal keratinocytes break; blisters heal without scarring.
- Junctional EB: laminin-332 or type XVII collagen; split in the lamina lucida; can be lethal in infancy.
- Dystrophic EB: type VII collagen (COL7A1) anchoring fibrils; split below the lamina densa; scarring, mitten deformities, aggressive squamous cell carcinoma.
- Porphyria cutanea tarda: uroporphyrinogen decarboxylase deficiency (acquired or inherited); triggers alcohol, hepatitis C, iron overload, oestrogens, HIV.
- PCT histology: cell-poor subepidermal blister with festooning (preserved dermal papillae) and thick PAS-positive vessel walls.
- Epidermolysis bullosa acquisita is the autoimmune counterpart against type VII collagen.

## What it is

Epidermolysis bullosa is a group of inherited disorders in which structural proteins of the epidermis or basement membrane zone are defective, so minor friction causes blisters. The level of the split depends on the protein: keratins in simplex, laminin-332 or type XVII collagen in junctional, type VII collagen in dystrophic forms. The porphyrias, especially porphyria cutanea tarda, cause blisters on sun-exposed skin because accumulated porphyrins generate damaging oxygen species when hit by light.

## Step by step

- PCT: uroporphyrinogen decarboxylase activity falls in the liver (often with iron, alcohol or hepatitis C).
- Uroporphyrin accumulates and reaches the skin through the blood.
- Visible light excites porphyrins, generating reactive oxygen species.
- Damage at the basement membrane zone produces fragile skin and blisters on the backs of the hands.
- Healing leaves milia, scars and hypertrichosis.

## Inherited epidermolysis bullosa

| Type | Protein | Level of split | Course |
| --- | --- | --- | --- |
| Simplex | Keratin 5 or 14 | Basal keratinocyte | Mild, no scarring |
| Junctional | Laminin-332, type XVII collagen, integrin alpha6beta4 | Lamina lucida | Severe forms lethal in infancy |
| Dystrophic | Type VII collagen | Below lamina densa (anchoring fibrils) | Scarring, contractures, squamous carcinoma |
| Kindler syndrome | Kindlin-1 | Mixed levels | Photosensitivity, poikiloderma |

## Clinical notes

- Dystrophic EB patients often die of squamous cell carcinoma in young adulthood.
- PCT: urine is reddish-brown; phlebotomy reduces iron.

## Memory aid

Read EB by the layer: simplex breaks the cell, junctional breaks the glue, dystrophic breaks the anchors and leaves scars.

## Test yourself

Think of the answer, then tap the question to see it.

## Which protein is defective in dystrophic epidermolysis bullosa?

Type VII collagen, the main component of anchoring fibrils.

## Which enzyme is deficient in porphyria cutanea tarda?

Uroporphyrinogen decarboxylase.

## Why does porphyria cutanea tarda affect sun-exposed skin?

Accumulated porphyrins absorb light and generate reactive oxygen species that damage the basement membrane zone.

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## Elsewhere in DurgiPedia

- [Basement membrane](https://durgical.com/en/histology/basement-membrane/)
- [Cell junctions: tight, adherens, desmosomes, gap, hemidesmosomes](https://durgical.com/en/histology/cell-junctions-tight-adherens-desmosomes-gap-hemidesmosomes/)
- [Uroporphyrinogen decarboxylase](https://durgical.com/en/biochemistry/enzymes/uroporphyrinogen-decarboxylase/)
- [Collagen](https://durgical.com/en/biochemistry/enzymes/collagen/)

## Connections

## Related 4

- [Pemphigus](https://durgical.com/en/general-pathology/pemphigus/)
- [Bullous pemphigoid and dermatitis herpetiformis](https://durgical.com/en/general-pathology/bullous-pemphigoid-and-dermatitis-herpetiformis/)
- [Hepatitis C: why it becomes chronic, and its extrahepatic disease](https://durgical.com/en/general-pathology/hepatitis-c-why-it-becomes-chronic-and-its-extrahepatic-disease/)
- [How a single gene causes disease: enzymes, receptors and structural proteins](https://durgical.com/en/general-pathology/how-a-single-gene-causes-disease-enzymes-receptors-and-structural-proteins/)

## Related conditions 4

- [Porphyria cutanea tarda](https://durgical.com/en/conditions/porphyria-cutanea-tarda/)
- [Epidermolysis bullosa acquisita](https://durgical.com/en/conditions/epidermolysis-bullosa-acquisita/)
- [Hereditary hemochromatosis](https://durgical.com/en/conditions/hereditary-hemochromatosis/)
- [Viral hepatitis](https://durgical.com/en/conditions/viral-hepatitis/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Epidermolysis bullosa simplex](https://medlineplus.gov/genetics/condition/epidermolysis-bullosa-simplex/) (MedlinePlus, US National Library of Medicine, 2025); [Dystrophic epidermolysis bullosa](https://medlineplus.gov/genetics/condition/dystrophic-epidermolysis-bullosa/) (MedlinePlus, US National Library of Medicine, 2025); [Porphyria: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/porphyria/) (MedlinePlus, US National Library of Medicine, 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/epidermolysis-bullosa-and-porphyria/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/epidermolysis-bullosa-and-porphyria/