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I have gone through your complaint and have seen the attached photograph (attachment removed to protect patient identity).
You are having herpes infection which is a viral infection.
You should try taking a course of antiviral like tablet Acyclovir 400 mg thrice in a day for 5 days and apply a topical antibiotic like Mupirocin on the affected area twice daily. This will resolve the lesion within 4-5 days.
This disease has a tendency to recur as the virus lives in the nerves of the host. Stress, ultraviolet radiation, surgery and infections can cause recurrence of the infection.
The Probable causes:
This viral infection is caused by herpes virus.Probable diagnosis:
Herpes labialisPreventive measures:
The recurrence of herpes infection can be prevented or reduced in intensity by the use of a sunscreen lotion on the lips. So once the lesion heals, start applying sunscreen on your lips.