Blisters are the most common warning sign. They can vary from small pinhead blisters to areas as large as the palm of a hand. The presence of any fluid behind a blister indicated a potential problem. If the fluid has a pungent, vinegary odor or feels greasy or sticky when rubbed between the thumb and forefinger, there is a high probability of osmosis. Identification of osmosis should be followed with immediate professional examination.