Amyloidosis of the skin is characterised by accumulation of eosinophilic, amorphous material (optical microscopy) subepidermally, within the papillary dermis. Usually focal degeneration of keratinocytes in the basal layer is present as well (amyloid is formed by keratin filaments from apoptotic keratinocytes).

In macular amyloidosis the amount of amyloid is low and epidermal reaction is not prominent. In lichen amyloidosus there is hyperkeratosis and acanthosis.

In nodular amyloidosis the light chains of immunoglobulins are accumulated.

In systemic (secondary) amyloidosis the amyloid accumulates within the walls of blood vessels.

Special stains are used for amyloid staining: congo red (brick red in transmitted light, polarisation, fluorescence); thioflavins (fluorescence); in nodular amyloidosis antibodies against light chains may be positive.