Myth Busters: Does a Red Mark After Gua Sha Mean Toxins Have Been Released?

The Claim

Among the most widely repeated explanations for the red or purple marking that appears after Gua Sha or IASTM is that the discolouration represents "toxins" being drawn out of the muscle to the surface of the skin, where they can supposedly be metabolised or excreted more easily. The darker or more extensive the marking, the story goes, the more toxic the tissue must have been beforehand.

It is an appealing explanation — visible, dramatic, and easy to communicate. It is also not an accurate description of what is actually happening in the tissue.

What's Actually Happening

The marking produced by Gua Sha — known in the traditional literature as sha — is a form of petechiae and ecchymosis: small, localised areas of bleeding from capillaries in the dermis and subcutaneous tissue caused by the shearing and compressive forces of the scraping tool. When a capillary wall is mechanically disrupted, red blood cells extravasate into the surrounding tissue, producing the visible red-to-purple discolouration. This is the same basic physiological event that produces an ordinary bruise, just induced deliberately and more diffusely across a treated area rather than from a single traumatic impact.

Once red blood cells sit outside the vascular space, the body initiates an entirely ordinary and well-understood clean-up process. Haemoglobin is broken down through a predictable sequence of pigments — contributing to the colour changes seen as a bruise evolves from red-purple to blue-green to yellow-brown over the following days — and the breakdown products are cleared by local macrophages and the lymphatic system. None of this involves "toxins" in any biochemical sense; it involves the normal clearance of extravasated blood, identical to what happens after any minor bruising injury.

Does It Do Anything Useful, Then?

This does not mean Gua Sha is physiologically inert — it means the commonly cited mechanism is the wrong one. Using laser Doppler imaging to directly measure tissue blood flow before and after treatment, Nielsen and colleagues found that Gua Sha produced a fourfold increase in local microcirculation that persisted for the better part of 25 minutes, accompanied by a reported reduction in myalgia both at the treated site and, in some cases, at distant sites (Nielsen et al., 2007). A more recent study using a different perfusion-measurement technique found a comparable 1.85-fold increase in local blood flow following treatment (Dubinskaya et al., 2023).

The authors of the original study were careful to note that the relief reported at distant sites could not be explained by local circulatory change alone, concluding that there is "an unidentified pain-relieving biomechanism" at work — very likely involving the same kind of broader neurophysiological pain modulation implicated in many forms of manual therapy, rather than anything resembling toxin removal.

The Verdict