By Fasusi Olayinka, BEng. (Env. Engrg), ISPON, OSHAssociation, NES, ISSS

Team Lead R&D, Marana Global Services Ltd. September 12, 2018.

In Nigeria and many countries in Africa, everyone understands how deadly mosquitoes can be.

This is why the use of many insect repellants (especially mosquito sprays) has become very popular as a way to control the vectors and prevent malaria. As good as this may sound, the question is, could there be higher risks to humans through the use of insecticides? Very likely, though, much research evidences are not available yet.

Many insect sprays in the Nigerian market, and of course, globally, have potential serious health implications if used without adequate caution.

Generally, insecticides and pesticides composed of pyrethroids (such as allethrin, tetramethrin, resmethrin, transfluthrin, prallethrin, cyfluthrin, permethrin, esfenvalerate, etc) as active ingredients. These are axonic toxins used in insect repellants. They are neurotoxic substances that are highly effective against insects, and may harm humans as well.

Some of them also contain carbamate propoxur and organophosphorus chlorpyrifos, as active ingredients. These substances may not pose significant concerns to human beings when used in low doses (WHO) but can harm sensitive individuals. Prolonged exposure (such as daily spraying and inhalation) to mosquito spray can cause headache, nausea, eye irritation, lung irritation and breathing problems.

At higher doses of inhalation or ingestion, common problems including tremors, dyspnea, and paralysis may occur. Also bear in mind that pyrethroids, especially permethrins are classified as possible carcinogens and the risk of bioaccumulation in humans has not been fully understood. Hence, frequent exposures should be avoided.


Even though, statistical information and scientific evidences are presently inadequate, it is advisable that people take more caution in the use of some of the chemically and biologically active household products in Nigeria.

Generally, consider the following.

  1. Cover food items and anything that can be contaminated before you start.
  2. Read the manufacturer’s instructions for use.
  3. Study the active ingredients and consult your material safety data sheet. DO NOT USE ANY PRODUCT OF WHICH SAFETY CANNOT BE ASCERTAINED. Ask an expert if necessary.
  4. Get your nose mask and eye goggles. This is recommended but many homes in Nigeria may find it difficult. To improvise, you can use a clean handkerchief. Double fold it to cover your nose and mouth before you spray.
  5. Open the windows and close only the window nets before spraying. The nets should prevent other insects from gaining entrance. As against some opinions that windows should be closed during spraying of insecticides, studies showed that most insecticides kill insects within seconds after contact. Opening the windows may not significantly reduce effectiveness of the spray.
  6. Use recommended spraying doses, and avoid looking up directly while spraying.
  7. After spraying, you should leave the room for at least, 1-hour before you ventilate. Natural air circulation should be adequate for ventilation.
  8. Even if the insecticide is odorless, bear in mind that some can be active up to 8-hours after spray.
  9. In case of direct contact with eyes or skin, follow first aid procedure recommended by manufacture. Seek immediate medical attention if you suspect any problem with the use of insecticides.


The research conducted by World Health Organization (WHO/PCS/RA/2005.1) contained some limitations. They concluded that more findings are required regarding pyrethroids. It therefore makes sense to take your safety as a priority when handling products like insect repellants and pesticides which contain pyrethroids.

Selected References,,;jsessionid=5693D637412ADDA4F5E9F7ACB2B9349E?sequence=1

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