Ocular redness following smoke inhalation, especially from cannabis, results primarily from the vasodilatory effects of certain compounds within the smoke. Specifically, tetrahydrocannabinol (THC), a primary psychoactive component, lowers blood pressure. This reduction in blood pressure causes blood vessels and capillaries to dilate, increasing blood flow to the eyes. The increased blood flow manifests as visible redness on the sclera, the white part of the eye.
The vasodilation caused by constituents of smoke has significant implications. While transient redness may be perceived as a minor cosmetic effect, it reflects a systemic physiological response. Understanding this response is valuable in contexts ranging from medical assessment to understanding the effects of smoke inhalation, including wildfire smoke. Historically, this visible physiological change has been a recognizable indicator, although the underlying mechanisms have only been elucidated through modern pharmacological research.