Caused by a common virus called herpes simplex (HSV-1), cold sores are contagious and can spread from person to person through skin-to-skin contact or by sharing items (such as eating utensils, lip balm, towels, cosmetics, and food), even when they aren't visible.
Infectious mononucleosis, or mono, refers to a group of symptoms usually caused by the Epstein-Barr virus (EBV). It typically occurs in teenagers, but you can get it at any age. People with mono often have a high fever, swollen lymph glands, and a sore throat.
Epstein-Barr virus (EBV), a widespread human herpes virus, can cause mononucleosis â but usually it doesn't. In fact, most EBV infections aren't noticeable, even when they're most active in your body. By age 35, almost everyone has antibodies to EBV, indicating past infection.