Deborah Blum | November
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
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
Photo courtesy: California Aggie
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
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:
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.
- 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
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.
In general, these are short term effects. Pepper spray, for instance,
induces a burning sensation in the eyes in part by damaging cells in the
outer layer of the cornea. Usually, the body repairs this kind of
injury fairly neatly. But with repeated exposures, studies find, there
can be permanent
damage to the cornea.
The more worrisome effects have to do with
inhalation – and by some reports,
California university police officers
deliberately put OC spray down
protestors throats. Capsaicins inflame the airways, causing
swelling and restriction. And this means that pepper sprays pose a
genuine risk to people with asthma and other respiratory
And by genuine risk, I mean a known risk, a no-surprise any police
department should know this risk, easy enough to find in the
scientific literature. To cite just three examples here:
1) Pepper Spray Induced
Respiratory Failure Treated with
Extracorporeal Membrane Oxygenation
2) Assessing the
incapacitative effects of pepper spray
during resistive encounters with the police.
3) The Human
Health Effects of Pepper Spray.
That second paper is from a law enforcement journal. And the summary for
that last paper notes: Studies of the effects of capsaicin on human
physiology, anecdotal experience with field use of pepper spray, and
controlled exposure of correctional officers in training have shown
adverse effects on the lungs, larynx, middle airway, protective reflexes,
and skin. Behavioral and mental health effects also may occur if pepper
spray is used abusively.
Pepper spray use has been suspected of contributing to a number of deaths
that occurred in police custody. In mid-1990s, the U.S. Department of
Justice cited nearly 70 fatalities linked to pepper-spray use, following
on a 1995 report compiled by the American Civil Liberties Union of
California. The ACLU report cited 26 suspicious deaths; it’s important to
note that most involved pre-existing conditions such as asthma. But it’s
also important to note a troubling pattern.
In fact, in 1999, the ACLU asked the California appeals court to
declare the use of pepper spray to be dangerous and cruel.
That request followed an action by
northern California police officers against environmental protestors –
the police were accused of dipping Q-tips into OC spray and applying them
directly to the eyes of men and women engaged in an anti-logging
“The ACLU believes that the use of pepper spray as a kind of chemical
cattle prod on nonviolent demonstrators resisting arrest constitutes
excessive force and violates the Constitution,” wrote association
attorneys some 13 years ago.
Yesterday, the University of California-Davis announced that it was
suspending two of the police officers
who pepper-sprayed protesting students. Eleven of those students were
treated by paramedics on scene and two were sent to a hospital in
Sacramento for more intensive treatment.
Undoubtedly, these injuries will factor into another scientific study of
pepper spray, another acknowledgement that top of the Scoville scale is
dangerous territory. But my own preference is that we start learning from
these mistakes without waiting another 13 years or more, without engaging
in yet another cycle of abuse and injury.
Now would be good.
About the Author: Deborah Blum is a Pulitzer-Prize winning science writer
and the best-selling author of The Poisoner’s Handbook: Murder and the
Birth of Forensic Medicine in Jazz Age New York. A professor of science
journalism at the University of Wisconsin, she blogs about chemistry
Speakeasy Science. Follow on Twitter