What causes fever blisters and what can u do to prevent them my ex husband never gets them what can I do to prevent them

Cold sores. Triggers for cold sores can include illness, stress, fatigue, becoming physically cold, dry air, uv rays (sun), mouth trauma or one's period. Mitigate any of these possible. Your doctor can prescribe valtrex (valacyclovir). Melissa officinalis or lemon balm (cream) has been shown in european studies to help expedite healing of cold sores. It can reduce healing time by half. Studies also show that regular use can.
Fever . Fever blisters also known as cold sores are caused by the herpes virus (most commonly herpes simplex type 1). They are spread by direct contact with the lesion when present. For example kissing when a lesion is present, having oral sex while the lesion is present, etc. Also sharing drinking glasses, soda cans, cigarettes, lipstick or chap stick can spread the virus. If all of he above can be avoided then the spread should be prevented. All the best.