Absolutely, says Lisa Conti, a veterinarian and director of the division of environmental health at the Florida Department of Health. "Dogs have bacteria around their mouths you don't want on your face." Every year, more than 200,000 Americans get stomach flu after ingesting a common bacterium found on the tail ends of dogs—and cats—called campylobacter. Another easily transmitted bacterium is salmonella, which causes diarrhea and fever in humans. The bugs get around thanks to the typical canine meet-and-greet sniffing, and an innocent kiss can pass it to you. "Dogs lick themselves all over, so these germs can be on the dog's nose when it's nuzzling you," says Peter Rabinowitz, MD, associate professor of medicine at Yale School of Medicine and an expert in pet-related infection.
Now that you're ducking dog kisses, you should probably plan to wash up after heavy petting. Soap and water are your best protection against ringworm, one of the most common infections dogs pass to people. A fungus like jock itch and athlete's foot, ringworm spores can lurk on a dog's coat or muzzle. Every year, ringworm makes the leap from pets to people an estimated 2 million times. Signs of ringworm include circular, scaly red patches on the skin. In dogs, the fungus can surface as hair loss or dry, flaky skin. "I'm not saying don't pet your dog," Rabinowitz says, "but I am saying to wash your hands afterward."
Less icky but no less irksome is poison ivy. Although the plant's tenacious oil won't bother Spot in the slightest, it can spread from his fur to your skin faster than you can say "no jump." So if you think your pooch came into contact with the plant after a frolic through fields and forests (maybe even the backyard), get out your gloves and give him a bath. "If it's low-growing ivy, you may be able to get by with just washing the dog's feet and legs," Conti says.