Brief Answer:
Not contagious, will heal in few days

Detailed Answer:
Hi XXXX
Welcome to health care magic.

Canker sores are small, superficial ulcers that appear in the mouth and make eating spicy foods uncomfortable.

These are most commonly caused by:
Stress or tissue injury
Certain foods including citrus fruits and vegetables (such as lemons, oranges, pineapples, apples, figs, tomatoes, and strawberries)
Sharp tooth surfaces like broken teeth
Ill-fitting dentures

They are commonly confused with cold sores which are caused by a virus herpes simplex.

These cold sores are highly contagious and usually occur on margins of lips and below nose.

I suggest you get a prescription for vitamin B complex capsules to be taken twice daily for a week.

You can get an over the counter anesthetic gel like Dentogel to apply over the canker sore 3-4 times daily.

These canker sores will heal by themselves within a week to 10 days.

Few tips to avoid recurrence of these sores:
Avoiding foods that irritate your mouth like citrus fruits and spicy foods.
Brush with a soft-bristled brush and floss daily.
Avoid ill fitting dentures.

I hope I have helped you with this answer.

Please let me know if I can assist you further.

Thanks.

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