Mushrooms can trigger eczema through a cross-reactivity pathway with airborne moulds. People sensitised to common moulds like Alternaria or Aspergillus (which many with eczema are, through environmental exposure) may also react to edible mushrooms because they share certain enzymes and proteins. This is called Fungus Food Allergy Syndrome — the mould sensitisation and the mushroom reaction may be the same immune response aimed at the same protein family, encountered through different routes (air versus food).

Not all mushroom species have the same allergen profile. Many heat-labile proteins in mushrooms are reduced by cooking, so thoroughly cooked mushrooms are generally better tolerated than raw. Dried mushrooms may concentrate allergens and are typically more reactive than fresh cooked mushrooms.