Dear Science Mine:
Why is a dog's nose cool and moist? — Mark Sharkey
Is it true that dog saliva has antiseptic qualities and is free from germs?
We have all heard at one time or another that one can judge the health of a dog by the temperature and dampness of its nose, and that letting a dog lick your wound will help it heal. I would call these old wives' tales if I wasn't an old wife myself.
Dogs' noses are moist because their tear ducts — nasolacrimal ducts — drain through their noses, and because dogs lick their noses a lot. Their noses are cool because they are moist, and the evaporation of moisture off a surface reduces the temperature of the surface.
Several Butte veterinarians assure me that you cannot judge a dog's state of health by feeling its nose. People often worry that their dog is ill because its nose is hot, not realizing that a dog's natural body temperature is higher than ours — usually between
101 F and 103 F.
Dogs do like to lick, and do not tend to be discriminating about where they put their tongues. Look at how they clean themselves (and other dogs, passing cats, garbage cans, rat cadavers and so on). This is why I am amazed that anyone would believe that dog
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saliva can clean wounds.
If dog saliva is an
antiseptic, dog bites would not become infected — but they do. Also, when one is
allergic to dogs, it is
actually saliva that triggers a reaction.
Dog saliva contains antigens that become airborne when dry, causing sensitive people to sneeze or worse. Furthermore, the licking of dogs can actually prevent wounds from healing, which is why veterinarians must sometimes go to embarrassing (for the dog) extremes to prevent dogs from
licking their sores.
However, some scientific evidence shows that dog saliva is not as nasty as it may appear. As with humans, one of the purposes of dog saliva is to bathe the inside of the mouth to float away food debris and keep oral bacteria in check. Studies have shown that enzymes in dog saliva can actually kill E. coli and Streptococcus canis bacteria, and that mother dogs lick their nipples to help keep their puppies free from disease.
A 1997 article in The Lancet, a respected medical journal, describes a study in which saliva-moistened surfaces were analyzed for nitric oxide to see if it is created when nitrites in saliva come in contact with the acidic surface of human skin. According to the authors of the study, the saliva-produced nitric oxide is "a powerful antimicrobial substance." They suspected that other compounds in saliva may be involved, but they nevertheless conclude that the reactions that occur when saliva meets skin can create natural antiseptic compounds.
The catch here is that though the authors quote anecdotal evidence of
people seeking to heal wounds with dog saliva, they used human saliva in their study. Dog and human saliva are similar and contain many of the same compounds. So if it was up to me, and I had absolutely no other antiseptics on hand, I would lick my own wound before I would let a dog do it. At least I know where my tongue has been.
Colleen Elliott is on the board of the Montana Mind Expansion and is the scientific editor for the Science Mine.
How does a GPS work? Why is the sky blue? Need to know? You ask the questions and Montana Mind Expansion — a group of Butte-area professionals and lay people with expertise in all fields of science and
engineering — will provide the answers. Send your most
perplexing query to The Science Mine, care of The Montana Standard, Box 627, Butte 59703; or Colleen Elliott, geological engineering, Montana Tech,