Cats Are Fine, Dogs Irritate My Eyes
Yesterday I went to someone’s home for a meeting, and their cat rubbed its head against me a lot.
Cats don’t seem to bother me.
Dogs sometimes make my eyes feel a little irritated, and I wonder whether it might be an allergy.
I looked into how cats and dogs differ.
Main allergens in cats and dogs
The proteins attached to fur, dander, and saliva cause animal allergies, rather than the fur itself. The main allergens have different names and come from different places: cats produce Fel d 1, while dogs produce Can f 1 and Can f 5.
| Cat | Dog | |
|---|---|---|
| Main protein | Fel d 1 | Can f 1; Can f 5 |
| Family | Uteroglobin | 1: lipocalin; 5: kallikrein |
| Produced in | Sebaceous, anal, salivary glands | 1: sebaceous glands; 5: prostate |
| Found in | Fur, skin | 1: fur, dander, saliva 5: urine, fur, dander (intact males) |
| Reaction rate among allergic patients | Up to 95% | 1: about half; 5: 26/37 in one study (70%) |
Uteroglobin, lipocalin, and kallikrein are protein families.
Fel d 1 is the first allergen identified from cats (Felis domesticus), and Can f 1 is the first identified from dogs (Canis familiaris).
I took the figures from Thermo Fisher’s allergen encyclopedia pages on cat dander, Fel d 1, dog dander, Can f 1, and Can f 5.
Fel d 1 in cats
Up to 95% of people with cat allergies react to Fel d 1. Cats produce it in their sebaceous and salivary glands, and grooming spreads it through the fur.
It travels on particles smaller than 5 micrometers (0.005 millimeters), which can float in the air.
Those fine particles can reach deep into the nose and bronchi, and Thermo Fisher’s encyclopedia associates them with asthma.
Even homes without cats can contain more than 8 micrograms of Fel d 1 per gram of dust, a level the encyclopedia describes as a marker of sensitization (detectable allergen-specific IgE, which doesn’t necessarily cause symptoms). Clothing can carry it indoors.
The encyclopedia says symptoms may take months to settle after a cat is removed from a home.
Male and female cats differ, too.
Neutering reduces Fel d 1 production to about one-third to one-fifth, suggesting a role for testosterone, a male sex hormone.
The encyclopedia says no cat is hypoallergenic: all living cats produce Fel d 1 regardless of sex, environment, breed, or age.
Can f 1 and Can f 5 in dogs
The WHO/IUIS registry lists eight dog allergens, from Can f 1 through Can f 8.
Can f 1, 2, 4, and 6 are lipocalins.
About half of people with dog allergies react to Can f 1.
It is secreted by sebaceous glands and gets onto fur, dander, and saliva.
Can f 5 is a prostate enzyme identified in 2009.
In a paper by Mattsson and colleagues, serum from 26 of 37 people with dog allergies (70%) reacted to Can f 5. Of those 26, 14 did not react to Can f 1, 2, or 3.
Because it is produced in the prostate, Can f 5 appears in male dogs’ urine and can also get onto their fur and dander.
According to the encyclopedia, people who react only to Can f 5 sometimes do not react to female dogs or neutered males.
I also wondered whether breed makes a difference.
Vredegoor and colleagues’ 2012 study compared Can f 1 on the fur and in the household dust of breeds marketed as hypoallergenic—Labradoodles, Poodles, Spanish Water Dogs, and Airedale Terriers—with Labrador Retrievers and a control group.
The supposedly hypoallergenic breeds actually had more Can f 1 on their fur, while the study found no breed difference in the amount in household air.
Differences between breeds were smaller than differences between individual dogs of the same breed.
The measurements did not support classifying any tested breed as hypoallergenic.
Why cats might be fine while dogs bother me
Different main allergens mean a person can be sensitized to one animal but not the other. Having no symptoms around a cat does not tell me whether I am sensitized to Fel d 1. My eye symptoms around dogs don’t tell me which dog protein, if any, is responsible.
Some cat and dog proteins are similar, though.
Dog Can f 6 and cat Fel d 4 are both lipocalins. Their amino acid sequences are 67% identical, and the two proteins cross-react enough to inhibit each other’s IgE responses (Can f 6).
Can f 1 and cat Fel d 7 are also 62% identical, and the source says they may cross-react.
This may be one reason some people become sensitized to both cats and dogs.
Having no symptoms around cats does not rule out sensitization to Fel d 4 and Can f 6.
In my case, dogs only make my eyes feel a little irritated. I have not tested which dog protein, if any, is involved.
The ImmunoCAP test list includes blood tests that measure specific IgE to Can f 1, 2, 3, 5, and 6 individually.
Test results alone do not establish the cause; a doctor considers medical history and symptoms as well. Which tests are available also varies by country and laboratory.
If someone is sensitized only to Can f 5, their symptoms may differ between intact male dogs and female or neutered male dogs.