Even if it’s a little icky, many people let their dogs lick their faces. Of course, there’s an obvious yuck factor, but are there actual health reasons to refrain from dog kisses? The answer turns out to be more complex than we expected. 
Dogs lick their owners for a variety of reasons. They may be playing, tasting, or seeking attention. Though there are many possibilities, Patty Khuly VMD told Vetstreet, “The bottom line is that most of the time, dogs will lick their people as a sign of affection.”
There are certain situations in which face-licking is definitely not okay.
There are a few instances in which experts agree that it’s not a good idea to kiss your dog. Shelly Rankin, PhD, an associate professor of microbiology at the University of Pennsylvania School of Veterinary Medicine, warned that babies, pregnant women, the elderly, and people receiving chemotherapy should beware of puppy kisses. 
These groups all have compromised or underdeveloped immune systems and may be more susceptible to disease transmission. Rankin added, “Anywhere the skin is broken, there’s potentially a risk,” which means if anyone in your family is struggling with acne, your pooch’s face-licking needs to be strictly discouraged.
Certain diseases can spread easily from dogs to humans.
A study published in the Archives of Oral Biology found that periodontopathic bacteria (which are basically disease-causing germs in the mouth) are transmitted between dogs and humans. Veterinarian Francoise Tyler told MSN that “If a pet has medical issues such as periodontal disease or intestinal parasites, there is a risk for cross-infection.” 
In an interview with People, Dr. Mehmet Oz pointed out that through scavenging, a dog could pick up giardia, hookworm, tapeworm, or salmonella. If you smooch your dog right after a walk, those germs could make their way onto your face or into your mouth. That being said, there may be some benefits from trading germs with your pets. A 2012 study showed that babies who lived with dogs had lower instances of respiratory illness. 
Of course, the dogs weren’t necessarily licking the babies in the study, so canine kisses still aren’t exactly vindicated.
Whether their kisses are dangerous or not, dogs’ mouths are grody.
“There is a myth that dogs’ mouths are cleaner than human’s mouths, and this is blatantly untrue,” Dr. Katy Nelson told Reader’s Digest. “The average American human brushes and flosses their teeth twice daily and I don’t know too many canines that live up to that.” 
Anyone who’s taken a dog on a walk knows that they stick their snouts in less-than-sanitary places. A garbage can that other dogs have peed on is one of the most desired sniffing spots, which should tell you a lot about dogs and hygiene.
But sometimes, a little dose of ick is a good thing.
Kim Kelly, a postdoctoral research associate at the University of Wisconsin-Madison, studies the possible health benefits of microbe transfer from dogs to humans. She believes that contact with dogs could have a probiotic effect on humans. 
In the course of her research, Kelly has found that adults who had contact with dogs had better immune systems and improved emotional well-being. However, it’s not clear exactly what causes those benefits. Kelly has heard anecdotes claiming that dog kisses have healed people but is also aware of cases in which dog saliva caused serious illness. She hopes to learn more about the health effects of trading microbes with canines, but for now she remains skeptical when it comes to whether kissing your pup is a good idea. 
“People need to be cautious,” she told USA Today. “We just don’t know enough at this point.”
