Allergies are common in people, and they can often accompany animal contact, triggering symptoms such as itchy eyes and sneezing.
But do allergies work the other way around? Can dogs and cats be allergic to us?
According to Dr. Heather Edginton, an assistant clinical professor of dermatology at the Cornell University College of Veterinary Medicine, our furry friends can have allergic reactions to people.
"The three main categories of allergies we see in dogs [and cats] are flea allergies, food allergies and environmental allergies," Edginton told Live Science. "An allergy to humans would fall in the category of environmental allergies."
Fortunately for many pets and animal lovers, allergy symptoms in pets are typically mild. Only very rarely are the symptoms dangerous or life-threatening. The most extreme allergic reaction animals (and humans) can experience is an anaphylactic reaction, Edginton said, which involves swelling, vomiting, seizures and even death in dogs and cats, according to the Merck Veterinary Manual. However, these severe reactions in pets are typically brought on by food allergies or bee stings, not by contact with humans.
Typically, when a dog or a cat is allergic to humans, its reaction is similar to the way a human who is allergic to dogs or cats might react. Usually, a dog or cat that is experiencing an allergic reaction will scratch repeatedly at otherwise healthy-looking skin. This condition is called atopic dermatitis, more commonly known as eczema. In felines and canines, eczema can be brought on by human dander, which includes dead skin cells and hair. Pets that are allergic to human dander and share indoor spaces with people will encounter it everywhere, including from carpets and vents.
And it turns out that, for pets with allergies, an allergy to humans is typically included. Of the roughly 20% of dogs that have symptoms of allergies, about half exhibit allergies to human dander. And while atopic dermatitis is common in cats, less is known about how frequently it is caused by human contact.
"When we do allergy testing [in dogs or cats], we find that they are usually allergic to 12 or more things at a time, and humans are often just one of those things," Edginton said. Other environmental allergies found in dogs include dust, pollen and mold spores, according to the review.
For pups with human allergies, there are several treatment options, such as administering preventative antihistamines, according to Edginton. This is often given as a pill and means the animal will need daily doses of the drug to stave off symptoms.
But not all pets respond to the drug.
"Ultimately, antihistamines only tend to be effective about 30% of the time," Edginton said. In 2015, Edginton and colleagues published a study on the effectiveness of the antihistamine loratadine, commonly known as Claritin, on 27 cats with skin allergies and found that the drug was generally ineffective.
Another treatment option is giving pets oral steroids such as prednisone.; According to the International Committee on Allergic Diseases of Animals, oral steroids in dogs tend to be more effective than antihistamines in treating acute allergic flare-ups as they happen, and they can also be used long-term therapeutically. However, side effects include lethargy, increased panting and increased hunger. Similar side effects are seen in cats.
A third option is allergen-specific immunotherapy, or allergy shots, according to the Merck Veterinary Manual, which involves injecting a pet that has allergies with controlled amounts of allergens to dampen the allergic reaction through exposure. This technique is effective in dogs 60% of the time, according to Edginton, and as much as 78% effective in cats.
Ultimately, allergies to humans can be treated but they can't be cured. "That's the thing with allergies in dogs," Edginton said. "Therapy is forever. Once you stop, the allergies will come back."
This article is for informational purposes only, and is not meant to offer medical advice.
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Cameron Duke is a contributing writer for Live Science who mainly covers life sciences. He also writes for New Scientist as well as MinuteEarth and Discovery's Curiosity Daily Podcast. He holds a master's degree in animal behavior from Western Carolina University and is an adjunct instructor at the University of Northern Colorado, teaching biology.