Coining, known in Vietnam as Cao Gio or “catch the wind,” is a traditional folk remedy practiced for centuries across various Southeast Asian cultures. The technique involves repeatedly rubbing the skin with a smooth, hard object, often a coin, until distinctive red or purplish marks appear. This practice is a form of therapeutic surface friction intended to address a range of minor health complaints.
The Traditional Practice and Intended Uses
The fundamental belief underlying coining is that many minor illnesses are caused by an imbalance or stagnation of energy, often referred to as “bad wind” or “heatiness.” Practitioners believe that vigorous friction draws this stagnant energy or blood to the surface, releasing it and restoring balance. The resulting marks confirm that the “bad wind” has been successfully expelled.
The practice is typically performed on large, muscular areas of the body, such as the back, neck, chest, and shoulders, where the friction is most intense. Before coining begins, a lubricating agent is applied to the skin, which is often a warmed medicated oil containing ingredients like camphor, menthol, or eucalyptus. Coining is traditionally used as a home remedy for common ailments like the cold, flu-like symptoms, fever, headache, muscle pain, and general fatigue or low energy.
The Physiological Mechanism of the Markings
The visible marks produced by coining result directly from intense, localized physical pressure and friction applied to the skin. The hard object scraping the surface causes mechanical stress to the underlying superficial capillaries. This physical force ruptures these tiny blood vessels just beneath the skin.
The extravasated blood leaks into the surrounding tissue, creating the characteristic linear patterns of bruising, known medically as ecchymoses or purpura. These marks are non-blanchable, meaning they do not temporarily disappear when pressed, confirming that blood has left the vessels and is trapped in the tissue. The vigorous rubbing also triggers an immediate, localized biological response.
This response includes localized vasodilation (widening of the blood vessels). Studies have shown that coining can increase microcirculation in the treated surface tissue by as much as fourfold in the initial minutes following the procedure. This increased blood flow persists for at least 25 minutes after the friction stops, indicating a substantial physiological change. Practitioners often correlate the intensity of the resulting discoloration with the severity of the illness being treated.
Scientific Evaluation of Therapeutic Efficacy
From a modern medical standpoint, coining is not a validated treatment for underlying diseases, lacking rigorous, large-scale clinical trials proving its efficacy. Research has explored physiological effects that may account for the relief reported by some individuals. The pain-relieving effect is often attributed to the principle of counter-irritation, where the brain shifts focus from internal pain to the localized, superficial discomfort created by the friction.
The increase in localized blood flow provides temporary symptomatic relief for muscle aches by facilitating the removal of metabolic waste products and increasing oxygenation. For fever, the pressure strokes and capillary dilation promote heat dissipation, similar to a tepid sponge bath. Smaller randomized controlled studies suggest that coining, or its Chinese variant Gua Sha, reduces chronic pain, particularly in the neck and lower back, due to the localized circulation boost and anti-inflammatory signaling.
The role of the placebo effect and cultural comfort is significant in the perceived benefit. Receiving a familiar, culturally accepted treatment from a trusted source can trigger the body’s natural pain-modulating responses. While coining may temporarily alleviate symptoms, it does not address the root cause of an underlying infection or systemic disease.
Safety Considerations and Medical Recognition
While generally considered safe by practitioners, coining carries several risks related to skin integrity and potential toxicity. Vigorous friction can cause minor skin abrasions, and if the tool is not properly sterilized, there is a risk of transmitting blood-borne pathogens. The practice involves medicated oils, and excessive use of camphor-containing products has been linked to toxic effects, including seizures.
A primary concern is the potential for misidentification by healthcare professionals unfamiliar with the practice. The linear, patterned ecchymoses on the back or chest can be mistaken for signs of non-accidental trauma or physical abuse, especially in children or vulnerable adults. This misinterpretation can lead to unnecessary medical investigations, social services involvement, and a breakdown of trust. To mitigate these issues, individuals who practice coining should inform their medical providers about the marks to ensure appropriate diagnosis and avoid unwarranted concerns about abuse.