Pets

Two collections, 147 articles, and the assumption that breaks between them

Everything in this section is about living with a cat or a dog. The Cat collection holds 124 guides and covers what an owner needs when something looks wrong: what normal breathing, drinking and sleeping actually look like in numbers, which signs need a veterinarian the same hour, and what the line items on an invoice mean. The Dogs collection holds 23 guides and is almost entirely about food, because almost every question a dog owner types is a quantity question wearing a yes or no costume.

This page covers the layer underneath both, and it exists because of one thing neither collection can own on its own. Veterinary safety information is species-specific in a way that human health information almost never is. An article about ibuprofen written for people applies to every person who reads it. An article about ibuprofen written for pets applies to exactly one species, and applied to the other it can be wrong in the direction that costs an animal a kidney.

That sounds obvious written down. It stops being obvious at eleven at night, in a household with both animals, when the search box returns a page that does not say which species it is about until the fourth paragraph. It also stops being obvious when the honest answer is that a substance is a nuisance to one animal and lethal to the other, which is the case more often than most owners expect.

Who lives in these households

The American Veterinary Medical Association publishes ownership figures from its Pet Ownership and Demographics Sourcebook, and the 2025 edition puts dogs in 42.6 percent of United States households and cats in 32.6 percent. That works out to roughly 56.3 million households with a dog and 43.1 million with a cat, holding about 87.3 million dogs and 76.3 million cats. The two groups overlap heavily, which is the practical reason this page exists rather than an abstract one.

Source: AVMA, US pet ownership statistics, drawn from the 2025 Pet Ownership and Demographics Sourcebook.

Two tools sit alongside these collections and they are deliberately separate rather than combined: the Cat Food and Toxin Safety Checker and the Dog Food Safety Checker. Building one tool with a species toggle was the obvious design and it was the wrong one, for reasons the next section covers. The rest of the pet calculators split the same way, down to separate age converters, because the aging curves are not the same shape either.

Four reasons a species difference exists, and how to tell which one you are looking at

Knowing that cats and dogs differ is not much use on its own. Knowing why they differ is, because the reason predicts whether a rule of thumb will transfer to a substance nobody has written a page about yet. There are four broad reasons, and they behave differently.

One: a metabolic pathway that is present in one species and weak in the other

This is the acetaminophen case, and it is the cleanest example in small animal medicine. Merck states that cats are especially susceptible because they have low glucuronyl transferase activity and therefore have limited capacity for glucuronidation. Glucuronidation is one of the main routes a liver uses to make a compound water-soluble so it can be excreted. When that route is narrow, the compound backs up into an alternative pathway that produces a reactive product, and the damage follows from there.

The numbers that come out of this are stark. Toxicosis in cats generally occurs at 40 to 50 mg/kg, and some cats have been reported to develop clinical signs at 10 mg/kg. In dogs, signs are generally not seen below 100 mg/kg. Even the presentation differs: cats tend toward methemoglobinemia, where the blood loses its ability to carry oxygen, while liver necrosis and jaundice are more common in dogs.

Two cautions belong with this. The first is that a narrow pathway is not an absent one, and the wording matters. Cats are described as having low activity and limited capacity, not none, and writing that cats cannot glucuronidate at all is a simplification that has been repeated into the pet-care internet as fact. The second is that this pathway does not explain every feline sensitivity, and it gets borrowed to explain sensitivities it has nothing to do with.

Two: a difference in how the red blood cells behave

This is the onion and garlic case. The compounds in Allium species cause oxidative damage to red blood cells, producing Heinz bodies and methemoglobinemia. Merck names cats as the most susceptible species, followed by dogs, and puts the figures at roughly 5 g/kg of raw onion for a cat against 15 to 30 g/kg for a dog. Garlic is described as 3 to 5 times more toxic than onion, which is why a garlic-heavy dish is a different question from an onion-heavy one even at the same weight.

Three: plain body mass, with no biology involved at all

The third reason is not a species difference in any interesting sense. A typical adult domestic cat weighs a fraction of what a typical adult dog weighs, so an identical amount of an identical substance arrives at a much higher dose per kilogram. Nothing about feline physiology is required to explain why a square of dark chocolate is a larger event for a 4.5 kg animal than for a 30 kg one. This reason is worth separating out because it is the one that scales predictably, and the one a reader can do the arithmetic on without any veterinary knowledge. Section 07 works through exactly that.

Four: nobody knows yet

The lily case belongs here, and it deserves to be said plainly rather than papered over. The effect is well documented, the species restriction is well documented, and the mechanism is not settled. There is no confidently identified toxic principle and no agreed explanation for why the kidney of a cat is affected and the kidney of a dog is not.

Grapes sat in this category for decades and only partly left it. Merck now names tartaric acid as one proposed toxic principle, following work published in 2022 that linked cream of tartar and tamarind ingestion in dogs to the same acute kidney injury. On cats, the same page is careful in a way that most pet-care writing is not: it records that anecdotal reports of renal failure in cats and ferrets exist, although there are no published case reports in these species. That is not a green light and it is not a red one, and the honest version of the sentence keeps both halves.

Same word, different disease

Toxicology is the half of this problem that gets attention. The other half is naming. Several conditions carry a name in one species that means something entirely different in the other, and the shared word does real damage because it makes an owner believe they already understand a diagnosis they have never heard explained.

Distemper

Feline distemper and canine distemper are not the same illness and are not caused by related viruses. Merck states it directly: feline panleukopenia is often referred to as feline distemper; however, the virus that causes disease in cats is unrelated to canine distemper virus that affects dogs and other carnivores. The feline disease is caused by feline parvovirus. Canine distemper virus is a paramyxovirus, described by the same source as closely related to the viruses of measles and rinderpest, which puts it in a completely different part of virology.

The confusion is not harmless. It leads owners to assume a dog vaccinated against distemper is protected against the feline disease, or that a household outbreak in one species threatens the other in the same way. Neither follows. The guide on feline distemper covers the disease itself, and the FVRCP guide explains which of the three letters in that combination shot covers it.

Parvo, where the relationship is real but only runs one way

This one is the opposite problem: the names are similar and so are the viruses, which makes the asymmetry easy to miss. Feline parvovirus is closely related to the canine parvovirus type 2 group. Merck records that currently circulating canine strains, CPV-2a, 2b and 2c, can cause clinically significant disease in domestic cats and in larger cats, while noting that feline parvovirus still causes substantially more feline enteritis worldwide than canine parvovirus does. And in the other direction, the same source states that feline parvovirus does not harm canids. The Merck entry on canine parvovirus adds the piece of history that explains the family resemblance: CPV is believed to have arisen from feline panleukopenia virus, which makes the dog disease the newer of the two.

So the crossing is one-directional. A dog cannot catch the feline virus. A cat can be made ill by the modern canine ones. That is a genuinely useful thing for a multi-species household to know, and it is precisely the detail that a page titled with one species in it will never mention. The feline panleukopenia guide covers what the illness looks like in a cat.

Viral identities and cross-species statements are quoted from the Merck Veterinary Manual entries for feline panleukopenia and canine distemper, reviewed June 2025 and updated March 2026 in the feline case.

Why rabies is in that table

Rabies is there as the control case, and it is the reason none of this can be reduced to a slogan about cats and dogs being different animals. Rabies is one virus, it affects both species and it affects people, and the advice really is the same across all three. A page about rabies exposure written for dog owners is not wrong for a cat.

The useful conclusion is therefore narrower than it first appears. Species transfer is not always broken. It is broken often enough, and unpredictably enough, that the only safe habit is to check whether the page in front of you says which animal it is about, and to treat an unlabeled page as one that has not thought about the question. The annual vaccine guide and the guide to what actually passes between pets and people both work through this in more detail.

Turning a milligram-per-kilogram threshold into something you can actually picture

Every published toxic dose in the sections above is expressed per kilogram of body weight, and that is the correct way to publish it. It is also the reason those numbers are hard to use. Nobody weighs the onion. What follows is the conversion, done both directions, so that the figures stop being abstract.

Direction one: how much of the thing does the threshold correspond to

Multiply the published threshold by the body weight of the animal. That gives the total amount at which the source says signs have been reported. Three worked rows, using a typical adult domestic cat of 4.5 kg and two dog sizes:

Arithmetic performed here on the per-kilogram thresholds quoted from Merck Veterinary Manual in sections 02 and 03. Body weights are illustrative round numbers, not published averages, and the correct weight to use is the one for the animal in front of you.

What that first row actually says

Roughly 23 grams of raw onion against roughly 450 grams. That is a twentyfold difference in the amount of the same vegetable, in two animals that live in the same house and both put their faces in the same dropped food. Twenty-three grams is a modest slice. Four hundred and fifty grams is most of a large onion, and a dog would have to work at it.

The acetaminophen row is the one to remember

An extra strength acetaminophen tablet sold over the counter in the United States contains 500 mg. In a 4.5 kg cat that single tablet is about 111 mg per kilogram, which is more than double the 40 to 50 mg/kg range at which Merck says toxicosis generally occurs, and about eleven times the 10 mg/kg at which some cats have been reported to develop signs. The same tablet in a 30 kg dog is under 17 mg/kg, which is well below the dog threshold. One object, two animals, two completely different situations, and no visible difference at the moment the tablet hits the floor.

Direction two, which is where the arithmetic usually collapses

Going the other way, from an amount eaten to a dose, requires knowing how much of the active substance is in the thing. That information is often simply not available. Xylitol is the clearest failure: sugar-free gum, mints, peanut butter and baked goods rarely state the xylitol content anywhere on the packaging, and the quantity per piece varies enormously between brands and even between flavors of the same brand. So the published 100 mg/kg threshold is precise, checkable, and frequently impossible to apply to the object in your hand.

The same problem shows up with chocolate, where the relevant compound is theobromine and the concentration depends on the type rather than the weight, and with anything homemade, where the recipe is the only record of what went in. This is a good reason to treat the phone call as the default rather than the fallback. The people who answer at a poison control service have the concentration data that the packaging does not carry, and they have it for brands as well as for categories.

If the animal in question is a dog and the question is a food, the Dog Food Safety Checker takes the food, the amount, the size of the dog and the symptoms and returns a first-pass estimate. For cats, the Cat Food and Toxin Safety Checker covers foods, plants, flowers, essential oils and household products in one place, which reflects how feline exposures actually arrive. Neither replaces the call.

Two collections, and which one you need

Each has its own hub covering the detail this page deliberately leaves alone. Counts are current as of 19 August 2026.

The tools, which split the same way

• Cat Food and Toxin Safety CheckerFoods, plants, flowers, essential oils and household products in one lookup, because feline exposures arrive from all five.
• Dog Food Safety CheckerFood, amount, dog size and symptoms, returning a first-pass estimate and a next step.
• Cat age converter and dog age calculator by weightSeparate tools, because the dog curve depends on size class and the cat curve does not.
• Cat vaccination scheduleFVRCP, rabies and FeLV dates by age, lifestyle and history.
• All pet calculatorsTen tools, including cost, weight, feeding and pregnancy for both species.

The other eleven sections of the site are on the blog hub.

The documents behind everything above

Every figure on this page is tied to the body that publishes it, with the review date where the source gives one, because veterinary reference material is revised and a number quoted without its edition is a number nobody can check. All links verified 19 August 2026.

• Lilies, cats and dogs. FDA, Lovely Lilies and Curious Cats: A Dangerous Combination, last updated 16 September 2021. Source of the statement about dogs, the trace-exposure routes, the three-day course and the 18-hour treatment window.
• Xylitol. Merck Veterinary Manual, Xylitol Toxicosis in Dogs, full review September 2024, last updated June 2025. Source of the statement that cats are not at risk, the 100 mg/kg and 500 mg/kg thresholds and the 30 minute to 18 hour onset range.
• Acetaminophen and other human painkillers. Merck Veterinary Manual, Toxicoses From Human Analgesics in Animals, full review July 2024, last updated May 2025. Source of the 40 to 50 mg/kg and 10 mg/kg feline figures, the 100 mg/kg canine figure, the glucuronyl transferase wording and the difference in clinical presentation.
• Onion and garlic. Merck Veterinary Manual, Garlic and Onion (Allium spp) Toxicosis in Animals, full review and last update September 2024. Source of the species susceptibility ranking, the 5 g/kg and 15 to 30 g/kg figures, the garlic multiple and the oxidative red cell mechanism.
• Grapes, raisins and tartaric acid. Merck Veterinary Manual, Grape, Raisin, and Tamarind Toxicosis in Dogs, full review September 2024, for the proposed toxic principle, the one grape per 4.5 kg guidance and the wording on cats and ferrets. The underlying work is Wegenast et al., Journal of Veterinary Emergency and Critical Care, 2022, volume 32, issue 6, pages 812 to 816.
• Feline panleukopenia and the distemper naming. Merck Veterinary Manual, Feline Panleukopenia, full review June 2025, last updated March 2026. Source of the unrelated-virus statement, the CPV-2a, 2b and 2c cross-infection statement and the statement that feline parvovirus does not harm canids.
• Canine parvovirus. Merck Veterinary Manual, Canine Parvovirus Infection, last updated June 2025, for the statement that CPV is believed to have arisen from feline panleukopenia virus.
• Canine distemper. Merck Veterinary Manual, Canine Distemper, for the identification of the virus as a paramyxovirus closely related to the viruses of measles and rinderpest. The susceptible species list on that page includes large felids, which is not the same as domestic cats, and the feline panleukopenia entry above is the one that settles the domestic question.
• Flea and tick products. AVMA, safe use of flea and tick preventive products, source of the quoted passage. Mechanism and clinical signs from Merck Veterinary Manual, Plant-Derived Insecticide Toxicosis in Animals, review August 2022, last updated September 2024.
• What poison control was called about. Pet Poison Helpline, Top 10 Pet Poisons of 2025, published January 2026, for both species lists and the acetaminophen commentary.
• Fees and numbers. Pet Poison Helpline for the $89 per incident fee and the inclusion of follow-up consultations, and ASPCA Animal Poison Control Center for the phone number and the fee wording. Read 19 August 2026.
• Ownership and spending. AVMA, US pet ownership statistics, drawn from the 2025 Pet Ownership and Demographics Sourcebook, for the household percentages, animal counts, per-household averages and per-household veterinary spending.
• Noted and not published. Several claims that circulate widely in this topic were checked and left out because no authoritative source supports them as stated: that cats cannot glucuronidate at all rather than having limited capacity, that grapes are established as toxic to cats, and a common explanation linking feline permethrin sensitivity to the same glucuronidation pathway as acetaminophen. Where a figure on this page is arithmetic rather than a published number, section 01 and section 07 say so on the line.