Herpes 1 is one of two forms of the herpes simplex virus that causes infection and disease in humans. It is most often responsible for labial or orofacial herpes, which causes sores to form on the mouth and face. Cases of genital herpes caused by herpes 1 are becoming increasingly common.

Herpes 1 usually causes painful, fluid-filled blisters to form on the mucous membranes of the affected area, most often the lips and mouth. Less commonly, blisters may form on other portions of the face. Orofacial herpes can also cause blisters inside the mouth similar to canker sores, resulting in inflammation of the gums and cheeks, sore throat, and fever.

In addition to orofacial and genital herpes, herpes 1 can cause whitlow, an infection of the fingers, toes, or cuticle. Another disease caused by herpes 1 is keratitis, an infection of the eye. Herpes keratitis causes inflammation of the eyelid and conjunctiva, the membrane covering the surface of the eye and the inner eyelids. It also causes itchy white lesions to form on the cornea, along with dryness, pain inside the eye, and sinus infection.

Herpes simplex virus invades and lives in the nervous system, and once a person has acquired it, he or she always has the virus, even if asymptomatic. Herpes type 1 has also been linked to Alzheimer's disease, or senile dementia. In people with a certain gene allele, herpes 1 increases the risk of developing Alzheimer's disease by weakening the nervous system.

Both herpes 1 and herpes 2 are spread by close contact, typically skin-to-skin contact. Herpes 2 is usually spread by sexual contact, but herpes type 1 may also be spread sexually, especially through oral-genital contact. Herpes type 1 is most easily spread if the infected person is currently experiencing symptoms, but it can also be spread when the infected person is not exhibiting any visible signs of the disease. Herpes type 1 may also be passed from a woman to her child during childbirth, and in such cases it may be fatal to the child due to an immature immune system.

There is currently no cure for the diseases caused by herpes 1, though there are treatments to prevent outbreaks or to manage symptoms during an outbreak. Medications addressing herpes symptoms may be injected or administered orally or topically. Treatments that help prevent outbreaks can also help prevent the spread of the disease.