hello and welcome to healthcare magic forum!
It happens when your hormonal
levels change or may be from any low grade fever
, it is caused by a virus to avoid getting it frequently try and follow the following steps :
Avoid skin contact with other people
Avoid sharing things, such as towels, lipstick, lip balm, cutlery, etc.
Follow good hand hygiene.
Avoid touching the sores. If you do, wash your hands with soap and warm water immediately.