HSV 1 also called oral herpes is a type of herpes that causes fever blisters or cold sores on the lips, gums, tongue and inside of the mouth, in rare cases it can cause genital herpes. This is typically transmitted when the infected person's open sore saliva comes in contact with another person.
Sources:
https://www.mayoclinic.org/diseases-conditions/genital-herpes/symptoms-causes/syc-20356161
https://www.cdc.gov/std/herpes/stdfact-herpes.htm
https://my.clevelandclinic.org/health/diseases/4248-genital-herpes-hsv-2
https://www.healthline.com/health/std/genital-herpes#when-to-see-a-doctor