The Facts on Pyrethroid Poisonings

What are pyrethroids? How do they work?

Pyrethroids are a form of insecticide. They are synthetic compounds, similar to naturally occurring pyrethrin insecticides derived from the flowers of the chrysanthemum plant. However, they persist in the environment longer and are more toxic than pyrethrins. There many pyrethroids, with permethrin being the most widely used. They are used to kill ants, fleas, flies, mosquitoes, and other insects. Pyrethrins and pyrethroids disrupt the insect’s nervous systems by interfering with nerve axons and prolonging sodium influx, resulting in paralysis and death.  

Are pyrethroids different than insecticides?

No, pyrethroids are a type of insecticide. Some pyrethroid formulations contain piperonyl butoxide, which is not an insecticide but enhances the pyrethroid’s activity.

Are pyrethroids toxic in humans?

Pyrethroids are much less toxic to humans than to insects because they do not bind as well to human sodium channels in the nervous system. Inhalation, contact with skin, or swallowing pyrethroids are ways pyrethroids can enter the body. However, they are not very well absorbed from the digestive tract or through the skin. Therefore, pyrethroids are considered less toxic than some other insecticides. They can cause irritation and allergic reactions, while high levels can cause more serious symptoms. Some spray formulations contain volatile hydrocarbon solvents or pressurized propellants which can also cause toxicity, especially if inhaled.

Is it safe to use pyrethroids indoors?

Yes, pyrethrins and pyrethroids can be used indoors. They can be applied as sprays and aerosol bombs. They are also found in insect repellants, pet shampoos, and lice treatments.

Symptoms of pyrethroid poisoning

Mucous membrane, skin, and eye irritation are the most common adverse effects associated with pyrethroid poisoning. If a person is exposed to a large amount of pyrethroid, they can develop nausea, vomiting, diarrhea, headache, dizziness, tingling, numbness, a “pins and needles” feeling, and muscle twitching. More serious effects, especially if large amounts are swallowed, include seizures, coma, and respiratory arrest. Inhalation can cause headaches, dizziness, runny nose, sneezing and itching. 

Contact with the skin can cause irritation, burning, redness, and tingling. In the eyes, pyrethroids can cause irritation, burning, itching, and corneal damage. Symptoms are most often due to an allergic reaction. If you are allergic to pyrethroids, you may develop a cough, shortness of breath, wheezing, difficulty breathing due to spasms of the upper airway, swelling in the mouth and throat, pneumonia, and possibly shock. People with asthma are more likely to experience wheezing and other respiratory symptoms after inhaling pyrethroids.

What to do if you inhale or come into contact with pyrethroids

If you inhale pyrethroids, you should leave the area immediately and seek fresh air to breathe. Open windows and air out the room. If you get pyrethroid insecticide on your skin, wash with soap and water. If you get a pyrethroid in the eye, rinse the eye with water for 15 minutes. If someone swallows a pyrethroid, gets pyrethroid in the eyes or on the skin, or inhales a pyrethroid, or if you have a question about using pyrethroids safely, help from experts is available through the webPOISONCONTROL online tool and by phone at 1-800-222-1222. Poison Control’s expert guidance is always free, confidential, and available 24 hours a day.
Wendy Klein-Schwartz, Pharm.D., MPH
Clinical Toxicologist 

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