Smiley Dental Lowell

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Fever Blisters & Ulcers

What is a cold sore?

Cold sore (or “fever blister”) is a cluster of small blisters that form on the lips (and can also form on other similar mucosal membranes). A cold sore is a type of herpes infection caused by the herpes simplex virus (HSV). The HSV virus remains in the body after an initial infection and reappears as a cold sore as stress or immune function is lowered.

Cold sores go through 5 stages before fully healing:

When to seek emergency dental care

What to do for fever blisters vs. ulcers

Fever blisters: These are viral, appear outside the mouth (around the lips), and are contagious. Inform your dentist if you have one prior to your appointment and they will likely reschedule any non-emergency treatment.

Canker sores: These are not viral, appear inside the mouth, and are not contagious. They can result from injury, stress, or eating certain foods. You may still want to delay a routine cleaning if the sores are very painful, but they will not harm the dental staff.

Should you go to the dentist with a fever blister?

No, you should not go to the dentist with an active, contagious cold sore and should reschedule your appointment. If the sore is already scabbed and healed, some dentists may see you, but you should always call ahead to be sure.

Frequently Asked Questions

Are cold sores contagious?

Yes. Avoid kissing, sharing utensils, or dental appointments when active.

Usually 7–14 days from start to full healing.

Yes. Stress, illness, or sun exposure often reactivates the virus.

No. Cold sores are viral and appear outside the mouth; canker sores are inside the mouth and not contagious.
Prescription antivirals, OTC creams, and avoiding irritants.

Schedule your Emergency Visit

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Call 978-999-9000 to book now.
Other locations: Boston 857-888-8000 • Beverly 978-288-1000 • Waltham 781-666-6000 • Fairhaven 508-967-1000