Why Are People Allergic to Dogs and What Makes a Dog Hypoallergenic?
What actually causes human dog allergies explains why "hypoallergenic" dogs can still trigger allergic reactions.
Each week, Dr. Patrick Tate, chief of the veterinary staff and a general practitioner at Webster Groves Animal Hospital, answers reader questions about pets. This week's question comes from Cynthia Shipman.
Question: Why are people allergic to dogs and what makes a dog "hypoallergenic?”
Answer: Many of my clients have asked the same questions, especially after the Obama family got Bo, their Portuguese Water Dog (Portie).
President Obama stated that they chose a non-shedding, “hypoallergenic" dog breed that could not trigger daughter Malia’s allergies. As a Portie owner and veterinarian, I have to respectfully disagree with the President! There is no such thing as a totally non-allergenic, non-shedding dog.
The true definition of hypoallergenic is “having a decreased tendency to provoke an allergic reaction.” The prefix “hypo” means less. Even though a dog is called hypoallergenic, it can still cause an allergic reaction in people who are sensitized. There is a lot of confusion and misinformation about this topic. It helps to understand what actually causes human dog allergies.
Allergic reactions to dogs are triggered by various proteins, referred to as "allergens." ALL dogs have allergens in their saliva, skin, urine and feces. The allergens stick to the dead skin flakes that dogs (and all mammals) periodically shed. This "dander" is mostly invisible to the human eye and easily transported through the air. Dander is also sticky and clings to clothing, bedding, carpeting, curtains, walls, etc. It can linger in a house for months after a pet leaves!
Interestingly, the two most common proteins that lead to an allergic reaction to dogs originate in the animal’s mouth. Canis familiaris 1 (Can f 1) is produced by the tongue epithelial tissue and Canis familiaris 2 (Can f 2) is produced by the tongue and parotid gland. The majority of human allergic reactions to dogs are caused by sensitivity to Can f 1.
When dogs drool or lick themselves, they transfer saliva to their fur and skin. The saliva dries and is released into the air – catching a ride on the animal’s dander. A dog’s saliva containing Can f 1 and Can f 2 can also be transmitted directly to the owner’s skin.
Dogs that are genetically “low-shedders” release less dander, and so are often called hypoallergenic or low-allergy. Even though the dog’s hair is not an allergen, when it falls from the hair follicle and sheds, it causes dander to be released. The more the dog sheds, the more allergen-coated dander is transferred into the home environment. (The dog’s hair can also carry other “outside” allergens like pollen, dust, mold, etc.)
ALL dogs shed their old hair in order to make room for the new. However, the hair of so-called hypoallergenic, low-allergy and low-shedding dog breeds grows more slowly and fewer hairs are shed at the same time, giving the false impression that the dog does not shed.
Dog hair grows in three phases: the anagen (growth phase), catagen (transitional phase) and teleogen (shed phase). Dogs like Portuguese Water Dogs, Poodles, Schnauzers, Soft-Coated Wheaton Terriers, Yorkshire Terriers, Maltese and others have an “anagen-predominant” coat. Their hair DOES eventually shed but about 90 percent of the time it is in the growth phase. As a result, they give off less dander and are called “low allergy.” (Their hair also grows much longer and they need a haircut like their andagen-predominant human owners.)
As you can see, some breeds might be called hypoallergenic, but none (even hairless dogs) are truly non-allergenic. Most people think that a hypoallergenic dog means no shedding and no allergens. Unfortunately, that is not true, despite what breeders and Bo’s owners may say.
For more information about allergies and animals, I recommend the book Allergic to Pets?: The Breakthrough Guide to Living with the Animals You Love, by Shirlee Kalstone.
The next Ask the Vet will answer the question “Which dog breeds are best for allergy sufferers and what should I do if I’m already allergic to my dog?”