Acaricide

by S. Serkan Sezer MD

Acaricides are chemical agents widely used in medicine, veterinary practice, agriculture, and public health for the control of mites and ticks. From the cream applied to treat scabies, to the collar fitted on a pet, to crop-protection products in agriculture, acaricides play an important — and often unseen — role in everyday life.

Definition

In English medical dictionaries, the term is transcribed as /əˈkærɪsaɪd/ and defined as “a substance which kills mites or ticks.”

More broadly, an acaricide is a chemical agent that kills, paralyses, or inhibits the reproduction of members of the Acari subclass — that is, mites and ticks. The term derives from the Greek akari, meaning “mite,” combined with the Latin suffix -cide, meaning “to kill.”

Acaricides are sometimes considered a subgroup of pesticides but are pharmacologically distinct from insecticides: mites and ticks are arachnids (eight-legged), not insects (six-legged), and they often respond to different agents.

History

The control of mites and ticks has occupied humans for centuries. Sulfur was one of the earliest acaricides used, and historical records show its application against scabies as far back as ancient Egypt and Rome. With the development of modern chemistry from the nineteenth century onwards, a wide range of acaricidal agents became available.

The DDT era of the twentieth century proved highly effective in the short term against mites and ticks as well as insects, but the environmental and health problems associated with it led to a search for safer alternatives. Modern acaricides are generally more selective, biodegradable, and less toxic to humans.

Acaricides Used in Medicine

In human medicine, acaricides are used principally in the treatment of skin disorders, above all scabies.

Permethrin

  • One of the most widely used acaricides today
  • Usually applied as a 5% cream
  • First-line treatment for scabies
  • Considered safe for use in children and pregnancy (under medical supervision)
  • Acts as a neurotoxin against parasites; in humans, applied topically, it has very low systemic absorption

Benzyl Benzoate

  • A long-established agent
  • Available as a 10–25% lotion or emulsion
  • Used as an alternative to permethrin
  • Can be irritant to the skin

Sulfur

  • One of the oldest and safest acaricides
  • Used as a 5–10% ointment
  • A particularly important option in infants, young children, and pregnancy
  • Has an unpleasant odour and can stain clothing

Crotamiton

  • Used as a 10% cream or lotion
  • Has both an acaricidal effect and an itch-relieving (antipruritic) action
  • An option in mild cases

Lindane (Gamma-BHC)

  • A powerful acaricide used in the past
  • Today largely banned or restricted in many countries because of neurotoxicity
  • Generally considered unsuitable, particularly in children and pregnancy

Ivermectin

  • An oral acaricide
  • Particularly useful in extensive or crusted (Norwegian) scabies
  • Used as a topical preparation against demodicosis
  • Considered one of the most important antiparasitic agents in modern medicine
  • The discoverers were awarded the 2015 Nobel Prize in Physiology or Medicine

Malathion

  • An organophosphate acaricide and insecticide
  • Used in some countries in the form of a 0.5% lotion against scabies and head lice
  • Use is restricted in some regions because of safety considerations

Acaricides in Veterinary Practice

The use of acaricides is even more widespread in veterinary medicine than in human medicine. Tick and mite infestations are major problems in pets, livestock, and birds.

Acaricides Used in Pets

  • Fipronil — spot-on, spray, and collar preparations
  • Imidacloprid — often used in combination with other agents
  • Selamectin — a member of the ivermectin family
  • Fluralaner — a relatively new, long-acting oral or topical agent
  • Afoxolaner — another modern oral product
  • Sarolaner — used against ticks and fleas
  • Amitraz — used in some preparations, but unsuitable for cats
  • Pyrethroids — for example, deltamethrin and permethrin (permethrin must never be used in cats)

Acaricides Used in Livestock

  • Amitraz — widely used in cattle and sheep
  • Cypermethrin and deltamethrin — pyrethroid-class agents
  • Flumethrin
  • Fluazuron — interferes with the growth of tick larvae
  • Ivermectin and doramectin — used as oral or injectable preparations

Application Methods

  • Pour-on — applied to the skin along the back
  • Dip — the animal is immersed in an acaricidal solution
  • Spray
  • Collars — release agent slowly over time
  • Ear tags — particularly used in cattle
  • Spot-on — applied to a small area of skin
  • Oral preparations — tablets, chewables, and similar formulations
  • Injectable preparations

Acaricides in Agriculture

In plant protection, mites are an important group of pests. Spider mites in particular can cause major losses in crops such as cotton, fruit trees, vegetables, and ornamentals.

Agricultural Acaricides

  • Abamectin — derived from the same family as ivermectin
  • Spirodiclofen
  • Bifenazate
  • Etoxazole
  • Hexythiazox
  • Propargite
  • Pyridaben
  • Fenpyroximate
  • Acequinocyl

Biological Acaricides

  • Predatory mites — for example, Phytoseiulus persimilis
  • Beauveria bassiana — an entomopathogenic fungus
  • Plant-derived oils — for example, neem oil
  • Soap-based products

Acaricides in Public Health

In public health, acaricides are used to control mites and ticks in the living environment:

  • Treatment of mattresses and furniture — for control of house dust mites
  • Garden and yard treatment — for tick control
  • Workplace and shelter treatment — for control of scabies outbreaks
  • Treatment of livestock buildings — control of mites and ticks affecting both animal welfare and human exposure

Mechanisms of Action

Different acaricides act through different biochemical and physiological mechanisms:

1. Effects on the Nervous System

Most modern acaricides act on the parasite’s nervous system:

  • Sodium-channel modulators — pyrethroids such as permethrin
  • GABA receptor modulators — fipronil, lindane
  • Glutamate-gated chloride channel modulators — ivermectin, abamectin
  • Octopamine receptor agonists — amitraz
  • Isoxazolines — fluralaner, afoxolaner, sarolaner

2. Effects on the Respiratory Chain

  • Disruption of mitochondrial electron transport — for example, acequinocyl

3. Effects on Growth and Development

  • Chitin-synthesis inhibitors — for example, fluazuron
  • Growth regulators

4. Physical Mechanisms

  • Sulfur and oil-based products work in part through physical effects on the parasite

Effective and Safe Use

The proper use of acaricides is critical:

Importance of Correct Diagnosis

  • The diagnosis should be confirmed before treatment is started
  • Lookalike conditions must be excluded
  • Identification of the species involved guides the choice of agent

Selection of the Correct Agent

  • Age and weight of the patient
  • Presence of pregnancy or breastfeeding
  • Other underlying conditions
  • Drug interactions
  • Local resistance patterns

Correct Application

  • Adherence to dosing instructions
  • Application time and frequency
  • Adequate area of skin treated
  • Repeated treatments where indicated

Treatment of Contacts

  • In conditions such as scabies, household members and close contacts should be treated at the same time
  • Environmental cleaning of clothing, bedding, and household items

Side Effects and Safety

Acaricides may produce a range of side effects:

Local Reactions

  • Skin irritation
  • Itching
  • Redness
  • Burning sensation
  • Allergic contact dermatitis

Systemic Effects

  • Headache
  • Nausea
  • Dizziness
  • In severe overdose, neurological symptoms

Risk Groups

  • Children — many acaricides require dose adjustment or are contraindicated below a certain age
  • Pregnancy and breastfeeding — agents with the most established safety profile should be chosen
  • Older adults — increased risk of skin reactions
  • Patients with skin disease — increased risk of absorption from broken or inflamed skin

Avoiding Pet Toxicity

  • Permethrin is highly toxic to cats
  • Amitraz is toxic to dogs in inappropriate doses and unsuitable for cats
  • Products formulated for dogs should never be applied to cats
  • Veterinary advice should always be sought

Resistance Problem

As with antibiotic resistance, mites and ticks can develop resistance to acaricides:

  • Particularly seen with intensive long-term use
  • Especially important in agriculture and veterinary practice
  • A significant issue for livestock ticks in some parts of the world
  • Resistance to permethrin has emerged in some areas
  • Resistance management strategies include rotation of agents, integrated pest management, and limited use

Environmental Impact

The environmental effects of acaricides are an important consideration:

Beneficial Organisms

  • Bees and other pollinators
  • Earthworms
  • Aquatic life
  • Soil microorganisms

Persistence

  • Some acaricides break down only slowly in the environment
  • Soil and water contamination
  • Risk of accumulation in the food chain

Sustainable Approaches

  • Integrated pest management (IPM)
  • Use of biological agents
  • Selective application
  • Use of natural products

Regulation and Approval

The use of acaricides is strictly regulated in most countries:

  • Approval of human medicines (e.g. by the FDA, EMA, or national health authorities)
  • Approval of veterinary medicines
  • Approval of agricultural pesticides
  • Pesticide-residue limits in food
  • Environmental impact assessments

Future Developments

Research and development in the field continue:

  • More selective new agents
  • Vaccines — particularly under development against ticks
  • RNAi-based technologies
  • Pheromone-based control strategies
  • Genetic-control approaches
  • Nanotechnology-based formulations

Practical Recommendations

For everyday use, the following principles are worth remembering:

In Human Health

  • Acaricides should not be used without proper diagnosis
  • Treatment should be carried out under the supervision of a healthcare professional
  • The full treatment course should be completed
  • Household contacts should be treated at the same time
  • Cross-contamination via clothing and bedding should be prevented

For Pets

  • Veterinary advice should always be sought
  • Products formulated for dogs and cats should not be interchanged
  • Dosing instructions should be followed strictly
  • Animals should be observed after application

In Agriculture and Gardens

  • Approved products should be used
  • Manufacturers’ instructions should be followed
  • Personal protective equipment should be worn
  • Pre-harvest intervals should be respected
  • The principles of integrated pest management should be applied

Disclaimer

The information provided here is intended for general informational and educational purposes only and does not constitute medical, veterinary, or agricultural advice. The use of acaricides should be undertaken under the guidance of an appropriately qualified professional (physician, pharmacist, veterinarian, or agricultural engineer). Inappropriate use can cause serious harm to human and animal health and to the environment. The treatment of any suspected mite or tick infestation should not be initiated without proper diagnosis. Do not rely on the content of this article when making decisions about your own or another person’s medical care.