Herpes simplex is a viral infection caused by two types of viruses, herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2). HSV-1 primarily causes oral herpes, characterized by cold sores or fever blisters around the mouth, while HSV-2 primarily causes genital herpes, characterized by sores in the genital or anal area. Both types can be transmitted through close personal contact and are highly contagious.