APPENDIX II-AN:  Sharma, Health hazards of mosquito repellents

and safe alternatives, CURRENT SCIENCE, VOL. 80, NO. 3, 10 FEBRUARY 2001 341


This appendix is copied from:




Health hazards of mosquito repellents

and safe alternatives

V. P. Sharma

Repellents such as vaporizers, diethy toluimide, and herbs are widely used in the country to combat

mosquito nuisance and malaria. A multicentric questionnarie-based study revealed that repellents

are harmful to human health, and their use should be avoided and discouraged. In this study 11.8%

people using various types of repellents complained of ill health effects, and some required medical

treatment. Although symptoms disappear shortly after withdrawl, those who do not suffer acute

toxicity symptoms and continue to use these repellents for extended periods may suffer neurotoxic and

immunotoxic hazards. Safe alternatives are discussed for use by the communities and local bodies.

IN most urban and rural areas of the country, mosquito

populations are menacing throughout the year, except for

some attenuation during summer and winter. Mosquitoes

transmit diseases such as malaria, filariasis and many viral

diseases such as the Japanese encephalitis, dengue haemorrhagic

fever, yellow fever (in Africa), etc. Mosquito coils

containing DDT and other organophosphorus compounds

were not effective in repelling mosquitoes. Buzzers and

electrocuting devices are also useless, just as mosquito

repellents1–4. Currently a variety of repellents are marketed

in India in the form of mats, coils, lotions and

vaporizers. These repellents use allethrin group of compounds,

herbs, oils or diethy toluimide (DEET). The

protection provided by these repellents generally lasts for

2 to 4 h.

Indian scenario

The current Indian market for various repellents is in the

range of Rs 500–600 crores (US $ 12–15 million) with

annual growth of 7 to 10%. This increase in growth rate is

the result of constant environmental degradation, leading

to the creation of mosquito-breeding grounds and also the

fact that people’s capacity to buy repellents is increasing

steadily. Marketing of repellents in India is well organized,

so that many brands can be found throughout the

country. Introduction of insecticides in the country is subject

to registration by the Central Insecticide Board, an

autonomous institution under the Ministry of Agriculture,

Government of India. Insecticides, for registration, should

be safe to human health, wildlife and non-target species.

Permission to market a product means that the product has

cleared the safety requirements as specified by the Central

Insecticides Board. Once the insecticide has been cleared,

there is no provision of post-monitoring the adverse

health effects of these insecticides, if any.

Health hazards due to mosquito repellents

Researchers are now providing data on the harmful effects

of repellents used against mosquitoes. The main site of

action of the pyrethroids is the sodium channel, which is kept

open for long periods of time, causing prolonged sodium

current to flow, leading to hyper-excitation of the nervous

system5. Synthetic pyrethroids, e.g. allethrin cause subnormal

or super-normal excitability by affecting the

sodium channel opening time. Cheng et al.6 exposed male

ICR mice to mosquito coil smoke with d-allethrin and

reported histopathological lesions, including the loss of

cilia and an increase in vascularity of the alveolar wall.

Liu and Sun7 reported that mosquito coils also contain

aromatic and aliphatic hydrocarbons, which are combustion

products of wood dust, fillers and dyes in the mats.

An exposure of rats to the mosquito coil smoke for 60

days resulted in focal deciliation of the tracheal epithelium,

metaplasia of epithelial cells and morphological

alterations of the alveolar macrophages. Liu et al.8 analysed

mosquito coils from Asia and South America and

reported that smoke from heating (or burning) contained

sub-micron particles (< 1 micron) coated with considerable

amount of heavy metals, allethrin and a wide range of

vapours such as phenol O-cresol. Furthermore, allethrin

used in the mats increased blood brain barrier (BBB)

permeability, suggesting a delayed maturity of BBB and

biochemical changes causing health risks, especially at an

early age in life9. Moya-Quiles et al.10,11 reported aggregation

of allethrin in the bilayer core. Eriksson et al.12 and

Ahlbom et al.13 reported changes in the density of muscarinic

acetylcholine receptors (MAChRs) in cerebral

cortex of mice treated neonatally with DDT, who later as

V. P. Sharma is in Malaria Research Centre (ICMR), No. 22, Sham

Nath Marg, New Delhi 110 054, India.




adults received bioallethrin, causing the irreversible

MAChR changes and behavioural disturbances. Johansson

et al.14 found behavioural aberrations in the adult mice

treated with bioallethrin. These findings are especially

important in view of high DDT deposits in the body of

Indian populations. Allethrin has no effect on insect

cholinesterase activity, but has stimulating action by

releasing acetylcholine (Ach) from the cholingeric ganglion15.

Diel et al.16 reported the immunotoxic properties

of s-bioallethrin caused by inhibiting lymphocyte proliferation

in a dose-dependent manner. D-transallethrin,

through hormonal pathways, may contribute to reproductive

dysfunction, development impairment and cancer17.

Results of questionnaire-based survey

Repellents use Type I synthetic pyrethroids. These insecticides

are heat stable and used in the treatment of mats,

coils and vaporizers, e.g. allethrin and bioallethrin 4%; dallethrin

0.2 to 0.3% w/w; d-transallethrin 0.1 to 0.15%

w/w; s-bioallethrin 1.9%, etc. On heating or burning of

mats and liquids, these compounds vaporize without

decomposition at temperatures up to 400°C and produce

repellent action on the mosquitoes. To study ill effects on

human health, we carried out a questionnaire-based survey

to elicit response from (i) users, and (ii) medically

qualified doctors. These surveys were carried out in the

urban and rural areas in 9 states by the scientific staff of

the Malaria Research Centre. Table 1 gives the results of

these surveys. Results revealed that 11.8% users comprising

all age groups and both sexes complained of a variety

of acute toxicity, either soon after or within a few hours

of use of repellents. Breathing problems were the most

common (4.2%) and frequently this condition was accompanied

with headache or eye irritation or both. Eye irritation

was the next common complaint (2.8%) and often it

was accompanied with bronchial irritation, headache or

skin reaction. Cough, cold and running nose was accompanied

with fever or sneezing in 1.67% cases. Some people

complained of wheezing and asthma and in 2 cases users

who did not have asthma became asthmatic, even after

discontinuing the use of repellents. There were complaints

of pain in the ear and throat. Of those using a DEETbased

cream, out of 174 people 20 (11.4%) reported skin

reaction, e.g. rash, black spot or in some cases skin turning

black or oily and itching, with 3 cases complaining

bad suffocating odour and eye irritation. Medical doctors

confirmed the reports of questionnaire-based household

surveys reporting adverse health effects. Out of the total

286 doctors interviewed from the same locations as the

household surveys, 165 (57.7%) reported acute toxicity

following the use of repellents. Doctors stated that

patients with strong reaction leading to asthma or bronchial

irritation, ENT or eye problems required treatment.

Menon and Halarnker18 warned against the use of repellents

and stated that: ‘Repellents – the Danger Within.

There could be danger from mosquito-repelling creams,

mats, oils and lotions. The principal class of chemicals

they use pyrethrums, could lead to running nose and

wheezing, prolonged use could lead to corneal damage,

asthma and liver damage, foreign studies warn. Indian

ENT surgeons are now reporting similar symptoms in

their patients. Not surprising, given our mosquito-ridden

cities.’ The Industrial Toxicological Research Institute,

Lucknow has also recorded serious health consequences

of the use of repellents19.

Alternative measures to combat mosquitos

There are completely safe alternate measures to the use of

chemical-based repellents. Use of these requires personal

attention, action by the community and the local bodies.

They are (i) Source reduction: weekly emptying and drying

of all standing water sources, howsoever small they

may be, in and around houses and other structures. Water

should be stored in containers that can be easily cleaned

and the opening should be well protected from the entry

of mosquitoes; (ii) Good drainage: proper gradient should

be provided to eliminate standing water in drains, lowlying

areas, ditches, borrow pits, etc; periodical de-silting

of drains, sewers and storm water drains before the onset

of monsoon to enable the drains to maintain steady flow;

(iii) Minor engineering works: overhead and underground

water tanks, wells and sumps should be sealed hermetically

and provided with ventilating shafts, made mosquito-

proof. Man hole covers should be in place;

(iv) Biological control: surface drains, temporary water

collections and scraps, etc. should be sprayed with Bacillus

thuringiensis H-14 at fortnightly intervals; larvivorous

fishes should be released in ponds, lakes, rice

Table 1. Results of questionnaire-based survey on health risks of

commonly used repellents


Number of people affected

out of 5920 persons



Breathing problem 248 4.20

Eye irritation 165 2.80

Cough, cold and sneezing 99 1.67

Headache 78 1.32

Asthma 28 0.47

Bronchial irritation 27 0.46

Itching 20 0.34

Ear, nose and throat pain 18 0.30

Others* 19 0.32

Total 702 11.80

*Giddiness, vomiting, nausea, allergy, etc.

Note: A variety of repellents were used routinely to protect from

mosquito nuisance. Of the total 5920 persons (including 286 medically

qualified doctors) interviewed, 5218 (88.20%) did not report any complaint

of adverse health impact in the use of repellents.



fields, drains, etc. (v) Personal protection methods: mosquito

nets, preferably treated with synthetic pyrethroid

insecticides (treated nets are safe); wire mesh doors,

windows and ventilators can be used; and (vi) Neem oil

can be extracted from the seeds of Azadirachta indica and

used as neem cream20; neem oil 5 parts and 95 parts edible

oil like coconut or mustard oil21 or mats treated with

neem oil22 or burning neem oil in kerosene23 would be a

cost effective alternative to chemical repellents. Neem oil

is safe when used as mosquito repellent24.

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Zasshi, 1995, 37, 5–8.

2. Belton, P., Mosq. News, 1981, 41, 751.

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7. Liu, W. K. and Sun, S. E., Toxicol. Lett., 1998, 41, 145–157.

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Biochem. Biophys., 1994, 312, 95–100.

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1993, 77, 21–30.

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1998, 251, 855–859.

18. Menon, S. and Halarnker, S., India Today, 25 May 1998, p. 70.

19. Seth, P. K., Industrial Toxicological Research Centre, Lucknow,

India, 1998 (pers. commun.).

20. Dua, V. K., Nagpal, B. N. and Sharma, V. P., Indian J. Malariol.,

1995, 32, 47–53.

21. Sharma, V. P., Ansari, M. A. and Razdan, R. K., J. Am. Mosq.

Control. Assoc., 1993, 9, 359–360.

22. Sharma, V. P., Nagpal, B. N. and Srivastava, A., Trans. R. Soc.

Trop. Med. Hyg., 1993, 87, 626.

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24. Valecha, N., Ansaari, M. A., Prabhu, S. and Razdan, R. K., Indian

J. Malariol., 1996, 33, 139–143.

ACKNOWLEDGEMENTS. I thank Dr Sarala K. Subbarao, Director,

Malaria Research Centre (MRC), New Delhi and the scientific staff of

the MRC field stations for the questionnaire-based surveys carried out

in various parts of the country.

Received 9 July 1999; revised accepted 13 November 2000