The Easy AnswerThe chance of contracting hepatitis from kissing is small because the viruses that cause hepatitis are basically spread through blood and bodily fluids (hepatitis B, hepatitis C, hepatitis D) and fecal-oral contact (hepatitis A, hepatitis E).
Quick Review of Hepatitis Viruses
The Not-So-Easy AnswerSince it's also been said that nothing in life is easy, maybe this question isn't as simple as we'd like it to be. The complexity comes from what is theoretically possible versus what is realistically probable. Realistically you're not going to get viral hepatitis from kissing. However it is theoretically possible. Since any type of direct contact with infected blood is a possible way to spread some of these viruses, there are kissing scenarios where the risk of exposure increases. I'll let your imagination wonder, but think about cold sores, cuts and prolonged kissing.
The Bottom LineIt all comes down to the level of risk you're willing to accept. Most of us regularly accept health risks of all kinds and levels in our lives. For example, we may drive a car, play contact sports, or smoke cigarettes. Obviously most types of kissing are completely harmless and won't allow any opportunity to spread the hepatitis viruses. For most people, the rare kissing scenarios that may allow some theoretical exposure to one of the hepatitis viruses will be risks worth taking.
Centers for Disease Control and Prevention. July 19, 2008. Viral Hepatitis B.
Centers for Disease Control and Prevention. July 10, 2008. Viral Hepatitis C.