Gua Sha is a home remedy practiced all over Asia. It is used for treating muscle pain and rigidity, respiratory conditions, cramps, spasms, blood stagnation, and many other conditions.
Gua means to scrape or scratch. The word Sha means sand, and refers to both the obstructed surface blood in the superficial muscles and to the reddish, raised rash that appears with the superficial frictioning. In Western medicine, this rash is called peticchiae.
To check for Sha, one applies finger pressure on the skin. If blanching occurs that is slow to fade then Sha is present. When working with clients, I always check for sha. We then discuss whether it is technique they are open to experiencing. Typically, Sha marks fade completely in 4-6 days.
See this article from Harper's Bazaar for a client's experience of Gua Sha.
For more detailed information on Gua Sha, Google Gua Sha and Arya Nielson.