Final answer:
The sores on the upper lip are caused by the herpes simplex virus type 1 (HSV-1), which leads to the development of cold sores or fever blisters.
Step-by-step explanation:
The sores on the upper lip in the image are caused by the herpes simplex virus. Specifically, these sores are commonly referred to as cold sores or fever blisters and are typically caused by herpes simplex virus type 1 (HSV-1). Although the virus can't be cured and remains in the body, antiviral drugs can help manage outbreaks. Cold sores can be very painful and are highly contagious, especially when the sores are visible, but the virus can also spread when no sores are apparent. It is important to note that this virus is different from the viruses that cause warts (human papillomavirus), chickenpox and shingles (varicella-zoster virus), and hand, foot, and mouth disease (coxsackievirus).