- Pitting edema is characterized by the presence of persistent indentation of the skin after applying pressure, due to the displacement of interstitial fluid into surrounding tissues.
- This occurs because the excess fluid in the interstitial space allows the skin to remain depressed for some time once pressure is released.
- In contrast, non-pitting edema shows firm swelling without indentation.
- The hallmark feature of pitting edema thus is the delayed rebound of the skin after pressure, reflecting fluid accumulation rather than solid tissue infiltration or inflammation.

Reference: Davidson’s Principles and Practice of Medicine, 23rd Edition, Chapter: Disorders of Fluid Balance and Electrolytes, Page 253.