New Delhi: Our first instinctive reflex when we see any kind of insect in our homes is to instantly spray it with bug-repellant. The strong-smelling sprays may do make you uncomfortable, but they do their job and the smell fades away after a while.


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However, scientists have meted out a warning saying that the smell fading away doesn't mean you get rid of the harmful chemicals too. In fact, chemicals present in bug- repellent sprays can linger in the dust in our homes for as long as a year, posing a health hazard – especially among children and pets – due to prolonged exposure to pesticides.


Warmer temperatures can lead to a flurry of unwelcome guests to our house – flies, mosquitoes, fleas, wasps, bedbugs and lice.


Pyrethroids are a common pesticide used to repel these pests, and even though they have been found more or less safe for mammals in laboratory studies, they can cause skin irritation, headache, dizziness and nausea for more sensitive individuals.


Since the active ingredients of household pesticides are often the same as those used in agriculture, researchers wanted to find out if laboratory studies are truly representative of what happens in a home.


Researchers from the the Biological Institute in Brazil found that when used outdoors, microorganisms, rain or sprinklers, and sunlight act to break down the pesticide's chemical compounds fairly quickly.


The chemicals in pyrethroid pesticides adhere to cloth, tiled floors and wood differently than they would to outdoor surfaces.


By running concurrent experiments – one in a controlled laboratory and the other in a test house - researchers found that the pesticides used in the controlled experiment broke down more quickly than those in the test house, with 70 percent of cypermethrin, a pyrethroid pesticide, still found in dust samples around the house after one year.


Researchers said that the persistence of pesticides inside buildings, on surfaces and in the dust in houses can be viewed in a couple of different ways.


On the one hand, when using pesticide products in the home, fewer applications should still maintain a long-term control of pests.


On the other hand, extended persistence increases the likelihood that residents will be exposed to the pesticide, which can be especially worrying for young children and household pets, who spend more time on the floor and are frequently picking up things and putting them in their mouths.


The findings, published in the journal Environmental Toxicology and Chemistry, highlight the importance of further studies to evaluate the actual risks of human exposure to pyrethroids when present in dust and on miscellaneous surfaces.


(With PTI inputs)