Bloodshot eyes are a pretty good indicator that someone is high. Here’s why this happens, and what you can do to prevent it.

One of the most distinguishing aspects of a marijuana high is those glaringly red eyes. Despite putting on perfume, washing your hands, and acting your heart out to look as normal and sober as possible, red eyes can easily break your cover. Fortunately, they are temporary and painless — they just make you look high as hell. Why does this happen?

Surprisingly, weed eyes have very little to do with the act of smoking, even if that’s what we usually associate them with. Weed eyes occur not only when you smoke weed; they occur when vaping and even with edibles, when there are no irritants like fire or smoke to contend with. This physical reaction occurs when your blood pressure drops and your heart rate increases, which is all due to the THC in your system.When your blood pressure drops, your blood vessels and capillaries dilate, including the ones in your eyes. This dilation increases blood flow, turning your eyes red and reducing intraocular pressure. Because of this, some experts believe marijuana could be a viable treatment for glaucoma.

Logic indicates that the redder your eyes, the more your blood pressure drops, and the more potent the THC. In other words, bright red eyes are usually a pretty good indicator of someone who is super high. While the smell may be masked and the user might be a seasoned cannabis consumer who knows how to handle a high, the eyes don’t lie.