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Table 1 Patch testing interpretation key

From: Cutaneous hypersensitivity reactions to freshwater cyanobacteria – human volunteer studies

+/-

Uncertain reaction: faint macular erythema only

+

Weak (nonvesicular) positive reaction; erythema, infiltration, possibly papules

++

Strong (vesicular) positive reaction; erythema, infiltration, papules, vesicles

+++

Extreme positive reaction; bullous reaction

-

Negative reaction

IR

Irritant reaction of different types

  1. Adapted from Rietschel & Fowler [16 (p. 24)] (interpretation key of the International Contact Dermatitis Research Group).