Herpes

Herpes is a contagious viral disease that results in sores in the affected area, usually the genitals or the lips. The disease is contracted through direct contact with an infected person, although a person may be contagious even if they are not showing the sores typical of the disease. Oral sores are quite common and apart from the discomfort, usually harmless. Genital sores are somewhat more serious. Although there's no risk of serious health complications, persons with genital herpes are at higher risk of cancers that affect the reproductive system (such as cervical cancer) and secondary infections, such as STDs and AIDS while they are suffering from an outbreak.
Herpes is incurable, but there are treatments to prevent outbreaks. These keep the virus in a state of latency, where it's neither contagious nor symptomatic. Herpes is very contagious when an outbreak occurs, and persons who come in direct contact with a person suffering from an outbreak are almost certain to become infected themselves. However, the virus does not persist in the environment for long, and it's impossible to get it from items that have been in contacted with an infected person.
Outbreaks are usually treated with anti-inflammatory creams that reduce the irritation caused by the sores. For mild outbreaks, application of a lubricant such as petroleum jelly will often alleviate the worst of the symptoms.