Are cold sores contagious?

According to WebMD, cold sores are caused by the herpes simplex virus, which is contagious. The virus is contagious via direct or indirect oral contact, which means that it may be spread by kissing, sharing cups or utensils, or sharing hygiene supplies such as towels and razors.

WebMD states that cold sores can appear as late as 20 days after exposure to herpes simplex virus. Cold sore attacks are usually signaled by itching, redness or pain near the exposure site. Approximately 90 percent of all American adults experience a cold sore at least once in their life, and 40 percent experience multiple attacks, according to WebMD.