Gua sha vents pathogens by intentionally causing therapeutic redness to surface on the skin. I often use this relaxing technique at the onset of a common cold by scraping the skin with a ceramic spoon or other smooth tool. 

Gua sha also produces an anti-inflammatory and immune protective effect that persists for days following a single treatment. This accounts for its effect on pain, stiffness, fever, chill, cough, wheeze, nausea and vomiting, and why gua sha is effective in acute and chronic internal organ disorders including liver inflammation in hepatitis.

The technique originated in East Asian medicine, and is now popular among physical therapists, athletic trainers, physicians, and nurses. This therapy is similar to the Graston Technique, commonly used in orthopedic medicine.