APPENDIX II-AN: Sharma, Health hazards of mosquito repellents
and safe alternatives, CURRENT
SCIENCE, VOL. 80, NO. 3,
This appendix is copied from:
CURRENT SCIENCE, VOL. 80, NO. 3, 10 FEBRUARY 2001 341
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
repellents14. 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.
The current Indian market for various repellents is in the
range of Rs 500600 crores (US $ 1215 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 peoples capacity to buy repellents is increasing
steadily. Marketing of repellents in
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,
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.
CURRENT SCIENCE, VOL. 80, NO. 3, 10 FEBRUARY 2001 342
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.
CURRENT SCIENCE, VOL. 80, NO. 3, 10 FEBRUARY 2001 343
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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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