Parliament committee calls for risk-based use of flea and tick treatment following Imperial evidence

The House of Lords Environment and Climate Change Committee has called for a more precautionary approach to the use of flea and tick treatments to reduce the number of unnecessary treatments across the United Kingdom. The report, published today, follows extensive evidence provided by Imperial experts warning of the overuse of these treatments and the environmental impact of year-round, preventative treatments.

Dr Tilly Collins, Deputy Director of the Centre for Environmental Policy, says:

“We are very pleased to have been part of the interdisciplinary collaboration that raised this topic to the House of Lords. The findings reflect many of our concerns and we are strongly supportive of their advice.”

“We want to do the best we can for our pets, for our homes and for the environment and this report reflects that.  We need to move away from overuse to appropriate use which reflects this balance.”

Imperial scientists also raised the alarm over the inclusion of these chemicals in monthly subscription schemes that encourage blanket treatment, irrespective of clinical need.

Dr Andrew Prentis, Veterinary Surgeon and Grantham Institute Fellow, says:

"The idea that you sign up to a subscription scheme and are automatically supplied with parasite treatments without testing or diagnosis is a bit like signing up to health insurance and then being supplied with year-round antibiotics just in case you get ill. You just wouldn't do it."

"Don't hesitate to ask your vet how often they are seeing cases of parasite infestation at this time of year in your region and about the environmental risks associated with using the treatments available."

The committee report, Paws for Concern: Pets, Parasites and Pollution, states that around 30% of dog owners and 20% of cat owners use year-round preventative treatments. There were an estimated 10.6 million dogs and 10.8 million cats in the UK in 2024.

Dr Rose Perkins, Research Fellow and member of the PREPP group says:

“The report highlights that the risks posed by pet parasite medications have been seriously underestimated. Our research has shown that these chemicals are contaminating homes, washing down drains and entering waterways at concentrations known to harm aquatic life. The evidence is clear: routine, preventative treatment of pets regardless of actual need is not scientifically justified, and this model has to change.”

What’s the harm? Flea treatments and the environment

Banned for agricultural use by 2018 due to their environmental impact, fipronil and imidacloprid are extremely toxic chemicals that are deadly to aquatic life, such as dragonflies. Any negative impact on species like dragonflies or mayflies can cascade through the food web to other species that feed on them such as fish and birds.

Professor Guy Woodward, Department of Life Sciences at Imperial College London’s Silwood Park campus, says:

“The evidence from laboratory trials about the harm these chemicals can cause is irrefutable and at the concentrations we are seeing in the wild we risk damaging our already threatened freshwater ecosystems.”

Due to overuse, these chemicals are now present in the UK’s waterways at levels toxic to wildlife. As a result, one of these chemicals, imidacloprid is now the number one chemical of environmental risk in many UK rivers.

Vet and author of Down the Drain, Dr Rose Perkins says:

“Multiple veterinary associations advise against routine blanket parasite treatments for pets, yet this practice remains common, particularly via subscription Pet Healthcare Plans. Many pet owners are not given sufficient information to make informed choices or provided with alternative options to routine continuous parasite treatment, such as an option to monitor and treat if needed.”  

What about human health?

There is concern around human exposure to the chemicals used in pet parasite medications, particularly those applied in spot-on treatments. Imperial researchers have shown that owners of treated pets may be exposed to these chemicals for prolonged periods after applying the products. However, the potential health impacts of this exposure are not well understood and more research is needed in this area. The Environmental Research Group at Imperial are looking at this issue, alongside human exposure to other pesticides used in the home.

This is just one of many areas where the potential impact of these products isn’t well understood and another reason to use these products cautiously and only when needed.

Dr Tilly Collins says:

“Recent research has quantified many of the risks to the freshwater environment, we now need a better understanding of potential impacts of long-term exposure to people.”

“We need to use these pesticides in a sensible way, both to reduce environmental and human exposure and to maintain their efficacity. They should be used only when the animal has an infestation or in a situation of high infestation risk.”

From homes to natural habitats: how flea treatments pollute our waterways

What researchers at Imperial have found is that the main pathway for these toxic chemicals to reach rivers is via pet owners: after applying flea medication to their dog or cats, residue from the medications is washed down the sink, either via handwashing, washing clothes or in the bathroom, into sewage treatment works and then into our rivers.

What Imperial experts advise

The PREPP - Producing Rational Evidence for Parasiticide Prescription group at Imperial College London advises a move away from routine, preventative treatments towards a more targeted use of flea treatments. The risk of fleas and ticks is typically lower in winter and spring than it is in summer and autumn. The PREPP team recommend that pet owners consider such risk factors including the lifestyle of their pet (e.g. whether their cat spends most of its time indoors) and consult a vet if they need advice.

Professor Leon Barron, from Imperial College’s Environmental Research Group, whose team have analysed water samples across most UK rivers, says:

“We’re calling for a change in the way we protect both our pets and the environment. Pet parasiticides are useful products to treat our pets, but only when they are at risk or are actually infested with fleas and ticks. Given the scale of use and the risks they pose to aquatic life currently, they need to be used appropriately and on a reduced scale to urgently reduce any environmental harm. It’s all about balance and is fixable, but we need everyone to realise that this is a major problem.”

Furthermore, rather than applying treatments directly to a pet’s fur, oral treatments often present a better, more effective and less environmentally harmful method for treating fleas. Alternative parasiticides to fipronil and imidacloprid include a group called the isoxazolines. These can be given to pets in a tablet form and have been shown to resolve infestations rapidly and without the need for household insecticide application. Isoxazolines, however, come with their own environmental risks so the group’s primary recommendation is to move away from preventative treatment towards a more risk-based approach.

Read the key recommendations from The House of Lords Environment and Climate Change Committee.

The recommendations of the committee will now go to the UK government for their response. In the meantime, the PREPP team will continue their research to further understand the impact of pet parasite medication on environmental and human health. This includes a 4-year fellowship commenced by Dr Rose Perkins at the Grantham Institute this week, which will aim to better understand human exposure and health risks from pesticides used in the home, including pet parasite medications.

The PREPP group at Imperial

The PREPP, Producing Rational Evidence for Parasiticide Prescription, group at Imperial is a multi-departmental collaboration of researchers that explore and evaluate the environmental risks posed by veterinary medicine pollution to gauge ecological impacts and to explore possible solutions.

Since mid-2022, the team's work has largely focused on the presence of pet parasiticides in urban waterways. This work was summarised in this Grantham Institute briefing paper published in March 2023.

The team is composed of researchers from the School of Public Heath, Department of Life Sciences, The Grantham Institute, and Faculty of Natural Sciences and reflects Imperial’s approach to convergence science.

Dr Andrew Prentis says:

"As a vet in practice, I had long been concerned that the scale of parasite treatment far outweighed the frequency with which we actually saw the parasites being treated. The work of our team at Imperial documenting the extent of environmental pollution with residues of these treatments has shown not only how important an issue this is, but also the importance of bringing together different disciplines for achieve useful and practical outcomes. This is what we call convergent science."