That's commonly called a (cold sore). It happens due to infection with a virus called (the herpes simplex virus). Have you ever had a blister like this before?
patient
半年前にも一度出ました。でも、受診するのははじめてです。
Yes, about six months ago. But this is the first time I've had it checked.
Once you get infected with the herpes simplex virus, (it lies dormant in the nerves) for your entire life. The virus can be reactivated and symptoms will start to show when your immune system is weakened. This can happen through catching a cold, working too hard, or being exposed to strong ultraviolet light.
I'm afraid not. The next time come and see me or another doctor as soon as possible after you feel any tingling or itching around your mouth. You can reduce the symptoms and stop the virus from spreading by taking the anti-herpes virus medicine at an early stage.
It's possible. It would be better to (avoid physical contact until the symptoms disappear). Be especially careful around babies, as it affects them more severely. Try not to touch the blister, (take your medicine conscientiously), and hope it heals soon.