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Pyrethrum vs Pyrethrin: Safety, Action, and Side Effects

by | Knowledge Bombs


In this article, we’ll tell you everything you need to know about the differences between pyrethrum vs pyrethrin. This includes their safety and possible side effects. Let’s see!

Whether you want to kill garden pests or household infestations, pyrethrum and pyrethrin should be among the safest insecticides.

In a nutshell, pyrethrins are the active chemicals found in the pyrethrum flower, which counts as a part-to-whole relationship. Despite their closely related nature, pyrethrum may be more dangerous than pyrethrin. Because the former can cause a series of allergic reactions. 

In this article, we’ll tell you everything you need to know about the differences between pyrethrum and pyrethrin, including their safety and possible side effects. Let’s see!


Pyrethrum vs Pyrethrin – What Are Pyrethrums?


Pyrethrums were initially used to refer to a group of flowers that belong to the Chrysanthemum genus. The two most famous flowers in this category are the Dalmatian Chrysanthemum and Persian Chrysanthemum. Both of which have yellow centers and white petals that make them seem like daisies.

Back in the day, ancient gardeners and farmers liked to grow these flowers to protect their produce against insects without using harmful chemicals.

With time, people started to crush pyrethrum flowers to make an insecticide ointment to control head lice, crab lice, and mites. Some authors believe the ancient Chinese were the first people to discover this treatment in 1000 BC.

Other cultures percolated the flowers with kerosene to extract a spray that can be used to kill home pests.


What Are Pyrethrins?


Pyrethrins refer to the active chemicals extracted from pyrethrum flowers. They’re the killing agents that directly interact with the nervous system of insects.

For years, people were using them without knowing anything about the underlying chemicals. It wasn’t until 1924 that scientists started exploring these chemicals. This paved the way for more potent insecticides.

Pyrethrins are more potent than raw pyrethrums. This is mainly because they’re more concentrated. Also, pyrethrin formulas contain several synergists. For instance, piperonyl butoxide (PBO), which inhibit the insects’ defense mechanisms, making them vulnerable to pyrethrins.

So, in short, we can conclude that pyrethrum is the total flower extract, whereas pyrethrins are the refined, more concentrated form.


Pyrethrum vs Pyrethrin: Mechanism of Action


As we said, pyrethrins are more potent than pyrethrums. However, that’s just a result of the refinement process. But in essence, both kill insects the same way.

To understand how pyrethrins work, we need to examine how nerve cells propagate sensations and motor impulses. But don’t worry, we’ll try to steer clear of the medical mumbo jumbo as much as possible.


How Nerve Cells Transmit Impulses



In the resting state, nerve cells are said to be polarized. That means that the molecules inside the neuron have a negative charge, while the outside molecules have a positive charge.

When an impulse reaches a nerve cell, it activates unique channels in the cell membrane. This allows external positive ions to enter the nerve cells. That process is known as depolarization. It reverses the charge. Now the inside is positive while the outside is negative.

The new positive charge starts traveling down neural pathways just like electricity travels through wires. After the charge passes forward, the special cell membrane channels thrust the positive ions outside the cells. This reverts the cell back to the resting state.


How Pyrethrins Kill Insects


Pyrethrins target the special cell membrane channels that we talked about earlier. After the channels pick up the positive ions, pyrethrins bind to those channels, making them unable to thrust the ions back outside.

That action is lethal to insects because it traps the nerves in the excited state, causing paralysis and general loss of motor coordination, which ultimately leads to death.


How Piperonyl Butoxide Helps Pyrethrins


Almost all insects have a natural safety mechanism that’s called mixed-function oxidase, but let’s name it MFO to keep things nice and simple.

The MFO system works by breaking down the toxins that insects pick up throughout the day, thus protecting them from permanent damage.

When the MFO system detects pyrethrins, it quickly breaks them down into ineffective molecules, meaning that they can’t cause paralysis anymore.

When piperonyl butoxide is added to the formula, it deactivates the MFO system, allowing pyrethrins to stay inside the insects for a longer time, wreaking irreversible havoc on the nervous system.


Pyrethrum vs Pyrethrin – Safety


Generally speaking, both pyrethrins and pyrethrums are considered to be safe insecticides, mainly because of their organic origin. However, that doesn’t mean they pose zero risks.


Pyrethrums Can Cause Severe Allergic Reactions


In 2000, a study reported that an 11-year-old asthmatic girl died after bathing her dog with a shampoo containing 0.2% pyrethrin. She had been using that shampoo for about two years, and her asthma has been worsening since then.

On the day of the incident, the girl experienced severe shortness of breath with wheezing. The medical team tried to treat the asthmatic attack for over 2 hours, but nothing worked.

Upon autopsy, the cause of death wasn’t attributed to pyrethrins, though. Doctors believed that the natural impurities found in the pyrethrum crude extract were the reason behind that aggressive allergy.


Pyrethrins May Cause Cancers


In 1999, the US Environmental Protection Agency (EPA) fed large doses of pyrethrin to rats to investigate its carcinogenic properties. Results revealed that male rats developed thyroid cancer, while female rats suffered from benign liver tumors.

But since humans won’t typically ingest pyrethrin in such large doses, the EPA concluded that pyrethrins aren’t human carcinogenic substances.

Other studies reported that farmers who used pyrethrins on their animals were more likely to develop leukemia. However, these findings aren’t accurate because those farmers use multiple pesticides — we can’t pinpoint the carcinogen in such cases.


Piperonyl Butoxide May Be More Dangerous Than Pyrethrins


The EPA also fed piperonyl butoxide to rats to determine whether it’s cariogenic or not. Like pyrethrins, results revealed that piperonyl butoxide might cause liver cancers, but it’s not a human carcinogen.

However, an alarming 2011 study found that if pregnant women directly inhaled piperonyl butoxide, children will have an impaired mental development.


The Takeaway: Pyrethrums and Pyrethrins Are Safe, But Within Limits


Based on the previous findings, it’s not risky to use pesticides containing pyrethrum and pyrethrin, but you must closely follow the label instructions.


Pyrethrum vs Pyrethrin – Potential Side Effects



If you don’t follow your product’s safety instructions, you may encounter one or more of these symptoms:

  • Headache
  • Tinnitus (ringing in the ears)
  • Nausea
  • Tingling of fingers and toes
  • Breathing problems

Children using pyrethrin shampoo may experience:

  • General irritation
  • Tearing
  • Burns
  • Itchy eyes
  • Blurred vision
  • Runny nose
  • Coughing
  • Difficulty breathing
  • Vomiting
  • Diarrhea

Dogs and cats may also show the following symptoms:

  • Drooling
  • Tremors
  • Uncoordinated movement
  • Difficulty breathing
  • Increased activity
  • Exhaustion
  • Seizures


Who Shouldn’t Use Pyrethrum and Pyrethrin?


Children should completely avoid using any pesticides, including pyrethrum and pyrethrin.

Pregnant and breast-feeding women can safely use these chemicals, but only when extremely needed. As we said earlier, pyrethrum and pyrethrin won’t do anything to your baby, but the other additives may hinder brain development.

Asthmatic patients and those who suffer from pollen allergy must completely avoid pyrethrum since it can cause a severe asthmatic attack.


Pyrethrum vs Pyrethrin – Final Thoughts: A Quick Word About Pyrethroids


Simply put, pyrethroids are the man-made version of pyrethrins.

Pyrethroids are generally safer than pyrethrins because they contain less active chemicals. As such, they’re less likely to cause allergic reactions. However, some studies suggest that pyrethroids may develop cancers upon long-term exposure.

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