Are Scoville Heat Units pretty much useless for pepper spray?

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Jul 24, 2006
I thought that knowing the effectiveness of your pepper spray would be good as far as strategies and tactics in self-defense. How many have come across the same findings as me? I'm doing research on what makes an effective pepper spray since they're obviously not all the same.

From almost everything I've found, the percentage of pepper extract, oleoresin capsicum, concentration of pepper spray, whatever you want to call it, is pretty much useless. If you have a pepper spray that's 10% oleoresin capsicum, the strength of the pepper oil that's actually in the spray can vary greatly and so the 10% doesn't tell you much. I've also seen quite a few sites and some studies published in scholarly journals saying that Scoville Heat Units are not reliable either. If you have a spray that's 2 million Scoville Heat Units, that's what the base resin is before it's mixed in with the propellant and carrier. The Scoville Scale is a taste test for how much it takes to dillute a pepper to the point you won't notice it anymore. If you have a pepper spray that's 2 million SHUs 1% Oleoresin Capsicum and another that is also 2 million SHUs but 20% Oleoresin Capsicum, the one that's 1% OC is going to be much more dilluted when it is actually sprayed out of the nozzle of the bottle. I saw a study by the University of Utah that found that since the Scoville Scale is a subjective taste test, and not a very scientific measure although it sounds that way, it can vary greatly from panel to panel. Many 2 million SHUs 10% OC pepper sprays would differ greatly in how hot they were from company to company. The same study found that even within the same brand from the same manufacterer, the hotness of pepper sprays would vary from batch to batch.

The University of Utah study found that the number one factor in determining effectiveness of pepper spray was the hotness of the spray, most reliably found by the capsaicinoid content. The same chemicals that make hot sauce taste hot is what makes pepper spray hot and painful. These are capsaicinoids, which include capsaicin (pure capsaicin is usually considered 16 million Scoville Heat Units) and other capsaicinoids (some of them less hot than capsaicin). According to this study, the true way to measure hotness is through a chemical test that calculates the % of the substance that is major capsaicinoids, or also known as % major capsaicinoids. The EPA for example, ignores SHUs and oleoresin capsicum % in regulating animal pepper sprays, but instead uses "Capsaicin and related capsaicinoids". After hotness of the spray, the University of Utah paper mentions the spray pattern and propellent that the pepper oil is in are both important in the effectiveness in pepper sprays. Here is a link to obtain a copy of one of the papers from the University of Utah professor:

Some say that you shouldn't look at percentage a major capsaicinoids because percentages don't count and only strength matters. They mix up oleoresin capsicum percentage with capsaicin and related capsaicinoids percentage. To see that there's actually a difference between the two, look at the picture below of the measurements on one of my favorite pepper sprays (you'll need to click it):
In other words, it's 15% 3 Million S.H.U. 3% Major Capsaicinoid Content. The 15% and 3% are completely different measurements. Most pepper sprays don't list the percentage of major capsaicinoids on their bottles, which has been criticized.
Addendum: Can I carry Pepper Spray and use it on my chili, if it's not hot enough? Or would I regret that?
I've sprayed quite a few pepper spray bottles and licked the nozzles. Some of them I like (I love hot Mexican food) and some of them are just painful to taste. It depends on the brand. Also, I've found out from first hand experience that getting sprayed directly into your eyes is much different than eating the stuff. When you spray someone in self-defense, you're not relying on them to say "Hey, this tastes bad! I'm going to leave you alone!"

The health of eating the stuff probably also depends on what the propellant and carrier materials are made of.
Beats me since i eat raw habeneros with a bit of sharp chedder as a tv snack . Howeaver the weak crap is bad in the eyes .. so is mace in the eyes . If it dont get into the eyes nothng will work , if it does even a spray bottle of amonia is worse than a finger .

Like a lot of other things, it is not one component, instead the sum of the components that determine the effectiveness.

Like motor oil, one cannot focus on just base oil, or add pack, or the amount of ZDDP, it is the sum of the whole.

Pepper Spray is the same way.

While the Scoville units are important, if the propellant decreases the Scoville units, or the sprayer has an in-effective spray, stream, or foam, or is difficult to know if the spray is going toward threat or you, ...
Sum of the whole

Some of the outdated Mace I have has a Dye that shows under UV light for instance. These still work, and yeah I keep them handy.
I used one to spray a vehicle that snagged a purse once, told the Police the make and model, and partial plate and UV.
It was a no brainer to find the exact car.

Same Mace is still sold, and one of my lady friends carries one, when youths ran out during a shoplifting, she was behind cover and got the pants of one.
It showed up nice under TB lights when the youths were marched right back into the store by the nice officer duty.

Effective. Perhaps depends on how one defines and what they expect.
Some of the outdated Mace I have has a Dye that shows under UV light for instance. These still work, and yeah I keep them handy.
I used one to spray a vehicle that snagged a purse once, told the Police the make and model, and partial plate and UV.
It was a no brainer to find the exact car.
Never thought of doing something like that. Effective indeed.

Re: Original post.
Sum of the whole, not individual components.

Reality is- there is no Holy Grail, No absolutes in Pepper Spray.
pax shared how a scrawny red headed girl was sprayed in a training exercise not affected much and ready to continue doing more training.
Others have share results all over the map, including they themselves being pepper sprayed.

Too many variables in life, that is the reality.
While we discuss, debate, and share, we just do not know what anyone will do.
Folks and critters do not know they are "supposed to be" affected a certain way, when sprayed, shot, hit with a baton - anything we do in defending and stopping an immediate threat.

I was doing a clinical rotation in a small , private mental health facility.
This 13 year old, went berserk on a med reaction, and bowled over two grown adults. They yelled at me to stop her, from going out a door, a door opened having supplies brought in.
I'm 6' and 170#. Oh I got a hold of her and matters went rodeo. I was holding onto to her and she was moving us both around pushing off walls, floors and ...
I know what it is like to grab a tiger by the tail...
or dance with a wildcat.

I've seen a skinny teenage kid on PCP , get hit with pepper spray - no affect, get hit with a baton, and I swear it looked like he never felt it, and dared to be hit again. Three big LEOs and they had their hand full!

We had a guy come into the ER, shot with Buck shot and he was cussing about his nice clothes being messed up.

Then again the fellow was like a linebacker, 6'4, and solid!
Cut his hand and at the sight of his own blood, fainted, I mean out like a light.

My take is, we cannot ever be so fixated and dependent on "something doing something".

Humans and critters do not know they are supposed to "react" a certain way, and then add any variables like a PCP hopped up perp, or rabies with a dog or raccoon.

Just my take...
Nothing's 100% effective, even high powered rifles. The reason I brought this up is not to bash certain pepper sprays (well kind of). It's just that if you're going to carry pepper spray, you might as well use something that will be the most effective out of the potential ones you could buy.
sm said:
Humans and critters do not know they are supposed to "react" a certain way, and then add any variables like a PCP hopped up perp, or rabies with a dog or raccoon.

This issue has been addressed before, regarding how people react to gun shot wounds differently, and the logical conclusion is that it doesn't matter, and it isn't even the question.

The question, what standard do we use to measure the effectiveness of pepper spray?

The question is important because once we know how to measure correctly, we will know when he have created spray so effective that is tears up the most resistant people under the most resistant of circumstances.

Similarly, if you were 6' and 230 pounds, that 13 year may have gone down in a second despite how amped up she was.
The question, what standard do we use to measure the effectiveness of pepper spray?

In the pepper spray class I took, we were taught to multiply the SHU by the OC % to get an at-the-nozzle effectiveness rating. This also gives you a common denominator to compare sprays with different SHU and percentage numbers:

2 million SHU @ 15% = 300,000
5 million SHU @ 4% = 200,000

Makes sense to me.

pax is correct of course.

I understand textbook material.
I also base some things on what I have seen with my own eyes.
In the Main OR of a hospital, I have seen the .22 short kill, and a man survive that stuck the barrel of a medium frame revolver in his mouth and pull the trigger on full house factory .357 loads.

Pepper Spray, I have seen a kid come into a ER, and at 8 y/o of age, the adults that brought her in said, she just put down the spray, and acted like she was more afraid of getting into trouble getting into the spray, than the effects of the spray itself.

She came into the house from garage and "Mom, dad, I messed up and am in real trouble I know, I didn't mean to...".

She went to get something out of the car, the spray in door pocket and being a kid, not in a good position to get what she went after...broke the beaded key ring, and bent the clip.
Stuck her finger inside the lid to fix the clip, and sprayed herself.

Pretty good spray too, as it startled her, and she kept her finger down instead of letting up.

Textbook is fine...Real World has too many variables.

Patients were supposed to make it, and died on the table.
Then again there was no way a patient was going to survive, and did.

I am not being difficult, I am not trying to be disagreeable. I am not trying to persuade anyone of anything.

Absolutes - if something begins life, someday life ceases.
Anything else is a crap shoot in my book.

Just how I was raised. Some say I am hard and cold.
I am a nice guy, read, study, pay attention and keep an open mind.
Me being me, I know the real world has too many variables, I choose to not subscribe and believe in everything I read in a textbook.

We used the cheapest spray perfume with a "good squirter" , soap and water solution in a "good squirter, and when aerosols came out, carb cleaner.
This before many on this board were born.

Soap in the eyes still works...sometimes. No Holy Grails.
Absolutely facscinating and interesting. Not to mention very important (I live in Illinois )

Just to further confuse the issue, I was taught in a class that the SHU tended to indicate rapidity of onset of effect(s) [If any :rolleyes: ] while the percent of OC tended to indicate the duration of the effects.

Instructor was a sheriffs training officer from Indiana, did not give a source.

Me, I got no clue :confused:

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