The Dangers of Pesticides & Herbicides

Chemical lawn treatments, weed-control products, insect sprays, and flea-and-tick products are part of many everyday environments. They are used in yards, parks, athletic fields, gardens, and even directly on pets. While these products are common, some contain chemicals that may raise health concerns for both people and dogs, including possible links to cancer risk. 

Why Lawn Chemicals Matter for Dogs and People

Dogs live close to us. They walk on the same grass, breathe the same outdoor air, lie on the same floors, and are exposed to many of the same household and environmental chemicals. Because dogs and people share similar environments, they may also share some of the same exposure risks.

Environmental pollutants, including herbicides and pesticides, have been studied for their possible role in cancer development in both humans and companion animals.

Understanding Pesticides

Pesticides are a broad category of chemicals used to control organisms considered pests. These may include insects, mites, spiders, flies, rodents, and some unwanted plants.

Pesticides are not only used outdoors. They may also be found in products used directly on dogs, including certain flea-and-tick shampoos, collars, dips, sprays, and topical treatments.

Some pesticide products may contain chemicals such as organophosphates, pyrethrins, and carbamates. These substances have been associated with a variety of health concerns, including effects on the nervous system and possible cancer-related risks.

Understanding Herbicides

Herbicides are chemicals used to reduce, manage, or eliminate unwanted plant growth. They are commonly applied to lawns, fields, parks, golf courses, and other outdoor spaces.

Two herbicides that often come up in health and environmental discussions are glyphosate and 2,4-D. Glyphosate is widely known because of its association with Roundup. 2,4-D is also notable because it was one of the ingredients used in Agent Orange, the herbicide mixture used by the U.S. military during the Vietnam War.

Dogs may come into contact with these chemicals by walking, rolling, lying, sniffing, or licking treated grass. These substances may also move into waterways, soil, and agricultural systems, which can contribute to broader environmental exposure.

How These Chemicals May Affect the Body

The potential effects of herbicides and pesticides vary depending on the chemical, the dose, the route of exposure, and how frequently exposure occurs.

Organophosphates are used in some pesticide products and can be toxic to mammals. They may interfere with normal neurotransmitter activity in the brain and nervous system, which can lead to symptoms such as tremors, muscle twitching, or convulsions.

Pyrethrins affect the central nervous system and may cause overstimulation, abnormal movements, weakness, or paralysis in cases of significant exposure.

Carbamates can also disrupt nervous system signaling. Exposure may result in muscle spasms, tremors, or seizures.

Because dogs spend so much time close to the ground, they may have more direct contact with treated surfaces than people do. They may also ingest residues when licking their paws, fur, or toys after being outside.

The Possible Link Between Lawn Chemicals and Canine Cancer

Researchers have studied whether herbicides and pesticides may contribute to cancer risk in dogs. The evidence is not always simple, and results can vary. Cancer risk may depend on many factors, including the type of chemical used, how often it is applied, how long the dog is exposed, the dog’s immune health, body condition, and breed.

Two cancers that have been studied in connection with herbicide and pesticide exposure are transitional cell carcinoma and lymphoma.

Transitional Cell Carcinoma

Transitional cell carcinoma, or TCC, is a form of bladder cancer that affects the lining of the bladder and urinary tract.

Some research suggests that herbicide exposure may be more strongly associated with TCC risk than insecticide exposure alone. Scottish Terriers have been studied in this area because they are already known to have an increased risk of bladder cancer compared with many other breeds.

In one study comparing Scottish Terriers with and without TCC, dogs exposed to lawn herbicides appeared to have a higher risk than dogs exposed only to insecticides as part of lawn care.

Other research has looked at topical flea-and-tick products containing ingredients such as fipronil or imidacloprid. In one study of Scottish Terriers, dogs exposed to certain topical flea-and-tick products were more likely to develop TCC than dogs that had not been exposed to these products.

Another study found that insecticide exposure may increase the risk of TCC, and that risk may rise with more frequent applications. In that research, dogs treated more often had a greater reported risk than dogs treated less frequently.

Canine Lymphoma

The relationship between insecticides, flea-and-tick products, and lymphoma in dogs is less clear. Many pet parents worry that flea-and-tick preventives may contribute to lymphoma, but studies have not consistently shown a clear connection between these medications and lymphoma risk, whether the products were topical or oral.

However, some research has found a stronger association between certain lawn-care chemicals and canine lymphoma. In one study, dogs whose owners used 2,4-D herbicides on their lawns were more likely to be diagnosed with lymphoma. The risk appeared to increase when the chemical was applied more often, especially with four or more applications per year.

How Much Exposure Is Too Much?

There is no single simple answer because exposure risk depends on several factors.

The amount of chemical exposure matters. Dogs who spend long periods on treated grass may have greater contact with residues than dogs who rarely visit treated areas.

Frequency also matters. Repeated exposure over time may increase risk compared with occasional exposure.

Breed may influence vulnerability. Much of the research on bladder cancer and lawn chemicals has focused on Scottish Terriers, which may already have genetic risk factors that make them more susceptible.

Body condition may also play a role. Some studies have found that overweight or obese dogs were overrepresented among bladder cancer cases connected with insecticide exposure.

Why Dogs May Help Us Understand Human Risk

Dogs can serve as important sentinels for environmental health because they share our homes, neighborhoods, and outdoor spaces. Some cancers in dogs resemble cancers in humans. For example, canine lymphoma has similarities to non-Hodgkin’s lymphoma in people.

Because of these similarities, studying cancer risks in dogs may also help researchers better understand how environmental chemicals could affect human health.

How to Reduce Your Dog’s Exposure

The best way to lower risk is to reduce the number of times your dog comes into contact with herbicides and pesticides.

Avoid using chemical lawn treatments in your own yard whenever possible. If you do treat your lawn, keep your dog away from the area for longer than the minimum label recommendation. Waiting at least 48 hours may be a more cautious approach.

Ask your local parks department, homeowners association, or recreation facility about the chemicals they use and when they apply them. This can help you avoid treated areas during higher-risk windows.

Consider herbicide-free weed-control options when possible. Some pet parents choose alternatives such as steam-based weed control, organic landscaping methods, hand-pulling weeds, or natural weed-control products.

Support lawn health naturally by using methods such as compost, overseeding, proper mowing height, and soil care to reduce the need for chemical treatments.

After walks or outdoor play, wipe your dog’s paws, belly, and legs with a damp cloth or pet-safe cleansing wipe, especially if your dog has been on public grass.

Bathe your dog regularly using a gentle, dog-safe shampoo to help remove residues from the coat and skin.

Feed a minimally processed, high-quality diet when possible. Highly processed foods may be more likely to contain environmental residues than fresh, organic, or lower-processed foods.

If you are concerned your dog has had significant chemical exposure, talk with your veterinarian before using binders or supplements such as activated charcoal, bentonite clay, humic acid, or fulvic acid. These should be used carefully and under professional guidance, especially if your dog takes medications.

When possible, reduce reliance on chemical-heavy topical products. Some pet parents explore more natural flea-and-tick support options, such as cedar-based or peppermint-based products, but these should be used with caution. Essential oils can be irritating or toxic if used incorrectly, so always choose dog-safe products and speak with your veterinarian before applying them.

Key Takeaways

Chemicals such as glyphosate, often known by the brand name Roundup, and 2,4-dichlorophenoxyacetic acid, also called 2,4-D, are commonly used on lawns and landscapes. These substances may pose risks to both humans and dogs.

A pesticide is a chemical designed to kill or manage pests, including fleas, ticks, insects, rodents, and other unwanted organisms. An herbicide is a type of chemical used to kill or control unwanted plants, such as weeds.

Lawn herbicides are not risk-free. Their potential impact may depend on how often they are used, how long a dog is exposed, and the amount of contact the dog has with treated areas.

Lawn pesticides may also contain ingredients that can negatively affect the body.

Many pesticide labels recommend keeping people and pets off treated grass for at least 6 to 24 hours after application. However, waiting longer may be safer. A 48-hour waiting period is often a more cautious choice.

Paraquat is frequently described as one of the most toxic herbicides. In the United States, it is restricted to use by commercially licensed applicators.

The Bottom Line

Lawn chemicals, herbicides, pesticides, and some pest-control products are common, but common does not always mean harmless. Dogs may be especially vulnerable because they spend time close to treated surfaces and may lick residues from their paws and fur.

While research is still developing, some studies suggest possible links between certain lawn chemicals and cancers such as transitional cell carcinoma and lymphoma. The safest approach is to limit unnecessary exposure, avoid chemical lawn treatments when possible, use safer alternatives, and talk with your veterinarian about the best parasite-prevention plan for your dog.

Small changes, like avoiding freshly treated grass, wiping paws after walks, and choosing a less chemical-heavy lawn-care routine, can help reduce your dog’s overall environmental burden.

References

Karthikraj R, Kannan K. Widespread occurrence of glyphosate in urine from pet dogs and cats in New York State, USA. Sci Total Environ. 2019 Apr 1;659:790-795. doi: 10.1016/j.scitotenv.2018.12.454. Epub 2018 Dec 31. PMID: 31096409.

Knapp DW, Peer WA, Conteh A, et al. Detection of herbicides in the urine of pet dogs following home lawn chemical application. Sci Total Environ. 2013;456-457:34-41. doi:10.1016/j.scitotenv.2013.03.0191.

Portier CJ. A comprehensive analysis of the animal carcinogenicity data for glyphosate from chronic exposure rodent carcinogenicity studies. Environ Health. 2020 Feb 12;19(1):18. doi: 10.1186/s12940-020-00574-1. PMID: 32050978; PMCID: PMC7014589.

Tindle AN, Krueger LM, Swafford B, Mani E, Danielson C, Labadie J, Trepanier LA. Genotoxic Herbicide Exposures in Golden Retrievers With and Without Multicentric Lymphoma. Vet Comp Oncol. 2025 Jun;23(2):246-256. doi: 10.1111/vco.13051. Epub 2025 Mar 21. PMID: 40114542; PMCID: PMC12082782.