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Scientific American: About Pepper Spray


-By Deborah Blum

November 21, 2011- One hundred years ago, an American pharmacist named Wilbur Scoville developed a scale to measure the intensity of a pepper’s burn. The scale – as you can see on the widely used chart to the left – puts sweet bell peppers at the zero mark and the blistering habanero at up to 350,000 Scoville Units.

I checked the Scoville Scale for something else yesterday. I was looking for a way to measure the intensity of pepper spray, the kind that police have been using on Occupy protestors including this week’s shocking incident involving peacefully protesting students at the University of California-Davis.

As the chart makes clear, commercial grade pepper spray leaves even the most painful of natural peppers (the Himalayan ghost pepper) far behind. It’s listed at between 2 million and 5.3 million Scoville units. The lower number refers to the kind of pepper spray that you and I might be able to purchase for self-protective uses. And the higher number? It’s the kind of spray that police use, the super-high dose given in the orange-colored spray used at UC-Davis.

The reason pepper-spray ends up on the Scoville chart is that – you probably guessed this -  it’s literally derived from pepper chemistry, the compounds that make habaneros so much more formidable than the comparatively wimpy bells. Those compounds are called capsaicins and – in fact – pepper spray is more formally called Oleoresin Capsicum or OC Spray.

But we’ve taken to calling it pepper spray, I think, because that makes it sound so much more benign than it really is, like something just a grade or so above what we might mix up in a home kitchen. The description hints maybe at that eye-stinging effect that the cook occasionally experiences when making something like a jalapeno-based salsa, a little burn, nothing too serious.

Until you look it up on the Scoville scale and remember, as toxicologists love to point out, that the dose makes the poison.  That we’re not talking about cookery but a potent blast of chemistry.  So that if OC spray is the U.S. police response of choice  – and certainly, it’s been used with dismaying enthusiasm during the Occupy protests nationwide, as documented in this excellent Atlantic roundup -  it may be time to demand a more serious look at the risks involved

My own purpose here is to focus on the dangers of a high level of capsaicin exposure. But as pointed out in the 2004 paper, Health Hazards of Pepper Spray, written by health researchers at the University of North Carolina and Duke University, the sprays contain other risky materials:

Depending on brand, an OC spray may contain water, alcohols, or organic solvents as liquid carriers; and nitrogen, carbon dioxide, or halogenated hydrocarbons (such as Freon, tetrachloroethylene, and methylene chloride) as propellants to discharge the canister contents.(3) Inhalation of high doses of some of these chemicals can produce adverse cardiac, respiratory, and neurologic effects, including arrhythmias and sudden death.

Their paper focuses mostly, though, on the dangerous associated with pepper-based compounds. In 1997, for instance, researchers at the University of California-San Francisco discovered that the “hot” sensation of habaneros and their ilk was caused by capsaicin binding directly to proteins in the membranes of pain and heat sensing neurons.  Capsaicins can activate these neurons at below body temperature, leading to a startling sensation of heat. Repeated exposure can wear the system down, depleting neurotransmitters, reducing the sensation of the pain. This knowledge has led to a number of medical treatments using capsaicins to manage pain.

Its very mechanism, though, should remind us to be wary. As the North Carolina researchers point out, any compound that can influence nerve function is, by definition, risky. Research tells us that pepper spray acts as a potent inflammatory agent. It amplifies allergic sensitivities, it irritates and damages eyes, membranes, bronchial airways, the stomach lining – basically what it touches. It works by causing pain – and, as we know, pain is the body warning us of an injury.

FULL STORY HERE:

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