Some pet owners worry about getting germs from their pets, but they need to be careful about what really unhealthy, and even poisonous, ingredients their pets can pick up from licking them.
Earlier this year I read that a commonly prescribed skin cancer cream, fluorouracil (sold as Carac, Efudex and Fluoroplex), killed five dogs who came into oral contact with the drug, either by ingesting it from the tube or by licking it off a human's skin. (source)
You may expect that a cancer treatment would be fatal to a dog or cat if ingested. But there are many, many other prescription and non-prescription skin creams and muscle rubs that we apply to our bodies every day that can be harmful to your pet. You don't think about this when your pet is licking you. You just think, 'Ah, how sweet!'
One thing that may shock you is that many bar soaps contain ingredients that are allergic to pets. Even hand sanitizers are harmful to your pet; if he inhales or ingests the isopropyl alcohol, he can develop aspiration pneumonia. Sunscreens or anything that contains zinc oxide are highly toxic, causing severe gastrointestinal distress. Muscle rubs contain various potentially harmful ingredients, including anti-inflamatories such as salicylates.
This list is not exhaustive, but here are some other common human skin products that may be harmful to your pet if licked:
Tea tree oil
Nail treatments, including nail polish and remover
Make-up and make-up remover
You also don't want your dog getting into anything you put in your hair or on your teeth. You should not use human shampoo or human toothpaste (or mouthwash!) on your dog or cat.
Most of the above products, if ingested by your pet, can lead to severe gastrointestinal reactions and/or seizures. If your dog responds with either of these reactions or others that are suspicious, take him to a pet emergency right away or to your vet's office.
Let me put it this way: there are many many more products that your dog or cat should not be licking from your skin, hair, or nails. So remove the remnants of any and all of them before you allow your dog to lick you.
Use a natural organic soap and check the soap's ingredients for pet safety; not all natural oils are safe for pets to ingest. (Please read this Meow Lifestyle article; it's about some natural oils that are bad for cats, but it also applies to dogs and other pets.)
One of the safest soaps for you to use on yourself is a baby-mild castile soap like Dr. Bronner's Pure Castile Unscented Baby Liquid Soap.
You can use a lightweight food grade mineral oil as a moisturizing skin treatment, but that's about it.
Though you can train your dog not to lick you, you will be denying her a pleasurable and reassuring activity.
BUT DON'T LET YOUR DOG LICK YOUR EYES, NOSE, OR MOUTH. THAT'S BAD FOR YOU!