Exposure to aluminum sulfate alters the allergen. Skin test results of three patients after 30 min are shown. Sample 1 contains cat allergen and water which was dialyzed against water and thus acts as a positive control. Sample 2 includes cat allergen and AS which was dialyzed against AS, thus the test sample contains AS. Sample 3 is cat allergen and AS which was dialyzed against water, therefore the test sample does not contain AS. Water and AS controls are also shown (samples 4 and 5 respectively). Representative photograph (patient 3) of skin test response after 30 min is also shown.