While fogging is helpful in killing adult mosquitoes with the dengue or Zika virus, it "would not be wise to conduct fogging indiscriminately" outside clusters, said Minister for the Environment and Water Resources Masagos Zulkifli yesterday.
He said his ministry has heard calls for fogging to be conducted at various housing estates, but stressed that routine fogging should not be used as a preventive measure.
He gave three reasons in his ministerial statement on Zika.
First, the fogging chemical has to come into direct contact with the mosquitoes to kill them.
This means fogging has to be carried out repeatedly and frequently as new swarms of mosquitoes continue to emerge from breeding habitats that have not been removed.
"Routine fogging is not a sustainable vector control measure," he said in Parliament.
Second, the right chemical and sufficient number of fogging guns need to be used to "achieve an effective kill".
Fogging just a single area may also chase mosquitoes to another location. This is why it has to be properly planned.
Third, the overuse or indiscriminate use of chemical treatment may increase the resistance of the local mosquito population. Owing to overuse, some insecticides are no longer effective, he said.
"I know everyone likes fogging because it's very optical - everyone can see it and everyone feels better. But it does not solve the problem."
Mr Masagos was replying to Mr Christopher de Souza (Holland- Bukit Timah GRC), who asked if fogging could be carried out in more areas.
The minister also said fogging is done as an extra measure to quickly stop the transmission of dengue or Zika.
His ministry's key strategy for dengue and Zika control is source eradication, which is to detect and remove breeding habitats and larvae.
"Fogging should be used only when there are Zika or dengue clusters or when the adult mosquito population is observed to be high so that we can mitigate the situation, which, again I qualify, is effective only (when done) together with source eradication," he said.