In contact eczema the dermal appendages
afford a mode of entry for the allergen into the epidermis
and dermis, causing changes in both these structures,
destructive in the epidermis and exudative in the dermis.
Oedema fluid and lymphocytes from the upper dermis then
force their way into the weakened epidermis to form
vesicles. The degree of the reaction varies considerably
in intensity from case to case.
Secondary sensitisation eruptions also have
their main impact on and around the dermal appendages,
as a result of which intercellular oedema and vesiculation
occur in the epidermis in relation to those appendages.
At a later stage in the secondary reaction, hypertrophy
of the sweat ducts takes place, and these hypertrophied
ducts adhere to one another in the upper dermis with