Abnormal thickening of the skin localized to the palm of the hand and the sole of the foot.

Blisters arising in the mouth.

The presence of one or more bullae on the skin, defined as fluid-filled blisters more than 5 mm in diameter with thin walls.

Cleavage within the epidermal keratinocytes, which is the innermost layer of the epidermis and consists of proliferating cells that give rise to the outer layers of the epidermis.

A type of blistering that affects the skin of the palms of the hands and the soles of the feet.

A type of blistering in which the lesions are located within the epidermis with loss of cell-cell adhesion of keratinocytes. In simplex EB, cleavage occurs in the basal layer, which is the innermost layer of the epidermis and consists of a single layer of basal germinative cells (mostly epidermal Keratinocytes) that proliferate and thereby produce new cells for other epidermal layers. As the cells move towards the upper layers of the epidermis they mature and eventually form cornified cells. The suprabasal cell layer lies directly above the basal layer and is composed of five to ten layers of cells.

Formation of lumps of tonofilaments, which are bundles of keratin filaments. In some but not all epithelia, keratin filaments are conspicuously bundled as tonofilaments. Inside the cell they braid the nucleus, span through the cytoplasm and are attached to the cytoplasmic plaques of the typical epithelial cell-cell junctions, the desmosomes.