Author: Dr Rosemary Perkins is a practising companion animal vet and Research Associate at the University of Sussex, with a PhD focused on environmental emissions from pet parasiticides. She is a member of Imperial College London’s PREPP group (Producing Rational Evidence for the Prescription of Parasiticides) and chairs Vet Sustain’s Pet Parasiticide Working Group. 

Flea, tick and worm treatments play an important role in keeping pets healthy. However, growing evidence shows that some of these products may also pose risks to the wildlife we care about, including the UK’s declining songbirds.

Flea, tick and worm treatments for pets - commonly known as pet parasiticides - are pesticides. Historically, it was assumed that the quantities applied to pets were unlikely to reach the wider environment in meaningful amounts. Recent research has challenged this assumption, demonstrating that residues from commonly used flea and tick treatments are entering the environment through multiple, previously unrecognised pathways. With more than 22 million cats and dogs in the UK, many treated routinely throughout the year, the potential for widespread environmental contamination is substantial.

Studies have shown that chemicals such as fipronil and imidacloprid - widely used in spot-on flea treatments but banned for agricultural use - are now being detected in unexpected places. Research funded by SongBird Survival found a high prevalence of these pesticides in bird nest linings, with a suspected association between pesticide exposure and increased chick mortality. Other studies have detected fipronil and imidacloprid in rivers and streams, particularly in urban catchments, at concentrations known to harm aquatic invertebrates. Wash-off from treated pets, including through bathing and dog swimming, has been identified as an important source of this pollution. Together, these findings show that everyday pet-care practices can create hidden and ongoing pollution pathways.

Importantly, it is possible to protect pets from parasites while also safeguarding wildlife. Responsible parasite control focuses on understanding whether treatment is genuinely needed and using products in ways that minimise environmental release.

A risk-based approach to parasite control

One of the most effective steps is adopting a risk-based approach. This involves targeting treatment to animals at higher risk of infestation or those with confirmed parasite burdens, rather than routine, blanket treatment. Veterinary organisations such as the British Veterinary Association (BVA) and the British Small Animal Veterinary Association (BSAVA) now advise against treating all pets for all parasites all of the time. Instead, they recommend assessing parasite risk on an individual basis, taking into account factors such as lifestyle, season, travel history and local parasite prevalence. Vet Sustain has recently launched guidance on responsible parasiticide use, including canine and feline parasite risk-assessment tools to support vets and pet owners in making informed decisions.

Routine parasite treatment should be avoided in lower-risk animals. For example, while flea exposure cannot be completely ruled out for indoor cats, their risk is substantially lower than that of cats with outdoor access. In such cases, regular flea combing with flea-dirt checks and prompt treatment if parasites are detected can be an effective alternative. Research also indicates that newer systemic isoxazoline treatments that can be administered orally or topically rapidly clear flea infestations, often without the need for additional household insecticide use, making this a viable strategy for many lower-risk pets.

Practical steps to reduce environmental risk

Pet owners can take several additional steps to use parasiticides more responsibly which can be discussed with your vet:

1. Swimming and bathing
If topical products such as spot-ons or collars are used, you should avoid allowing your pets to swim for the full duration of the product’s activity. Datasheet recommendations on post-application swimming intervals may help reduce emissions, but these are often precautionary defaults rather than product-specific, evidence-based values. Topical products should also be avoided in pets that are bathed frequently.

2. Talk to your vet about alternative treatments  
Many environmental concerns are associated with topical spot-on formulations, which can be washed off during bathing, swimming or routine household activities. Where appropriate, oral or injectable treatments may be preferable, as they are less likely to disperse directly into the environment.

3. Responsible disposal of pet faeces
Many parasiticides - particularly those administered in tablet form - are excreted in faeces. Pet waste should always be bagged and disposed of in bins to prevent environmental contamination.

4. Faecal parasite testing
Routine faecal testing for intestinal worms can help target treatment more effectively and reduce unnecessary use of worming products.

5. Disposal of applicators and pet hair
Used spot-on applicators and treated pet hair should be disposed of carefully to reduce the likelihood that wildlife, including nest-building birds, is exposed to pesticide residues. Pet fur can be disposed of in the bin rather than outside, and packaging or unused products can be returned to veterinary practices for proper disposal.

By adopting a more considered, evidence-based approach to parasite control, pet owners can continue to protect their animals’ health while also reducing unnecessary chemical exposure to the environment and the wildlife that depends on it.

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