They all contain insecticides called pyrethrins used in ancient Persia. Today, we use them in lice shampoos.
Welcome to JSTOR Daily’s detox series, where we consider how to limit exposure to substances considered unsafe by scientists. So far, we have covered flame retardants in milk, plastics in water, plastics and chemicals in digital detoxification. Today, we trace the origin of lice shampoo to ancient Persia.
In the past few years, schools across the country have been fighting the invasion of head lice. In 2017, in Harrisburg, Pennsylvania, more than 100 children were found to have lice, which the school district called “unprecedented.” And in 2019, a school in the Sheepshead Bay section of Brooklyn School reported an epidemic. Although the Centers for Disease Control and Prevention generally believe that lice are not harmful to health, they can be a major trouble. To get rid of lice and larvae (their small eggs), you need to wash your hair with an insecticide-containing shampoo.
The insecticidal ingredients in many over-the-counter shampoos contain a compound called pyrethrum or pyrethrin. The compound is found in flowers such as tansy, pyrethrum and chrysanthemum (often called chrysanthemum or chrysanthemum). These plants naturally contain six different esters or pyrethrins-organic compounds that are toxic to insects.
It was noticed that these flowers had insecticidal effects hundreds of years ago. In the early 1800s, Persian pyrethrum chrysanthemum was used to get rid of lice. These flowers were first grown commercially in Armenia in 1828, and were grown in Dalmatia (today Croatia) about ten years later. The flowers were produced until the First World War. This plant performs well in warm climates. In the 1980s, the production of pyrethrum was estimated to be about 15,000 tons of dried flowers per year, of which more than half came from Kenya, and the rest came from Tanzania, Rwanda and Ecuador. About 200,000 people worldwide participate in its production. The flowers are hand picked, dried in the sun or mechanically, and then ground into powder. Each flower contains about 3 to 4 mg of pyrethrin -1 to 2% by weight, and produces about 150 to 200 tons of pesticides per year. The United States began to import powder in 1860, but domestic commercial production efforts were not successful.
In the early days, pyrethrum was used as a powder. However, starting from the early 19th century, mixing it with kerosene, hexane or similar solvents to make a liquid spray is more effective than powder. Later, various synthetic analogs were developed. These are called pyrethroids (pyrethroids), which are chemicals that have a similar structure to pyrethroids but are more toxic to insects. In the 1980s, four pyrethroids were used to protect crops-permethrin, cypermethrin, decamethrin and fenvalerate. These newer compounds are stronger and last longer, so they can persist in the environment, crops, and even eggs or milk. More than 1,000 synthetic pyrethroids have been developed, but there are currently less than twelve synthetic pyrethroids in use in the United States. Pyrethroids and pyrethroids are often used in combination with other chemicals to prevent their decomposition and increase lethality.
Until recently, pyrethroids were considered quite safe for humans. In particular, it is recommended to use the three pyrethroid compounds deltamethrin, alpha-cypermethrin and permethrin to control insects at home.
But recent studies have found that pyrethroids are not without danger. Although they are 2250 times more toxic to insects than vertebrates, they may have harmful effects on humans. When scientists at the University of Iowa examined the health data of 2,000 adults to understand how the body breaks down pyrethroids, they found that these chemicals triple the risk of cardiovascular disease. Previous research has also found that prolonged exposure to pyrethroids (for example in people who package them) can cause health problems such as dizziness and fatigue.
In addition to people who work directly with pyrethroids, people also come into contact with them mainly through food, by eating fruits and vegetables that have been sprayed, or if their houses, lawns and gardens have been sprayed. However, today’s pyrethroid pesticides are the second most commonly used pesticides in the world. Does this mean people should worry about washing their hair with pyrethrum-containing shampoo? A small amount of washing is unlikely to harm humans, but it is worth checking the ingredients on the pesticide bottles used to spray houses, gardens and mosquito-prone areas.
JSTOR is a digital library for scholars, researchers and students. JSTOR Daily readers can access the original research behind our articles for free on JSTOR.
JSTOR Daily uses scholarships in JSTOR (a digital library of academic journals, books and other materials) to provide background information on current events. We publish articles based on peer-reviewed research and provide this research free of charge to all readers.
JSTOR is part of ITHAKA (non-profit organization), which helps academia use digital technology to preserve academic performance and advance research and teaching in a sustainable manner.
©Ithaca. all rights reserved. JSTOR®, the JSTOR logo and ITHAKA® are registered trademarks of ITHAKA.