Poison ivy is common throughout the vast majority of the United States. Most humans are quite allergic to the plant, which grows pretty much everywhere except in deserts and at high altitudes. Dogs rarely are allergic to poison ivy, but humans can get a rash from a dog that has come in contact with poison ivy.
How it works
Poison ivy has a sap running through it called urushiol oil. Humans are very allergic to this oil and will break out in an extremely itchy rash with a lot of red bumps or blisters after brushing up against the plant. Humans can even break out after the oil is transferred from someone who has contact with it, or from a pet, such as a dog, who has gotten some of the oil on its fur.
If your dog has been exposed to poison ivy, the urushiol oil is on the dog's coat and can spread to human beings. Rubbing alcohol can break down the oil. Put it on the dog's fur but avoid its face and genitals. Then rinse the dog off with a garden hose for at least 10 minutes. After drying the dog, rinse yourself off in cold water and wash your clothes. Use cold water on your skin, because hot water will cause the pores to open up and can cause a worse reaction to the oil.
It happens only rarely, but if a rash does occur on the dog, treatments are available to help out with the itching. To help the dog avoid licking the itchy area, a cone around his head may be necessary.
Jewelweed, also known as impatiens or touch-me-not, can be used to help with the itching. It is a common weed that you can mash up and apply to the affected area. Some people even use the mashed up plant to wipe off the urushiol oil. You can also apply a cold compress to the area and allow a fan to cool it. The cooling helps prevent blisters and oozing, which speeds up the healing process.
If there is a severe reaction with a lot of swelling, or if the dog has vomiting or diarrhea, seek veterinary care immediately.