Canadian Skin Patient Alliance
Merck Manual
Canadian Pharmacists Association
Cold Sores
Cold sores are caused by the Herpes Simplex Virus. The cold sore is the body's visible reaction to the Herpes Simplex Virus and appears as clusters of small blisters on the lips, around the mouth (especially the corners), and occasionally inside the nose. The virus is highly contagious and can be transmitted through contact, such as kissing, sharing utensils or towels, even when no symptoms are present.
More information about cold sores
Individual cases are not reportable to the Health Unit.
Should one go to childcare, school, or work if they have cold sores?
No exclusion necessary for simple cold sores. Children who attend school or childcare that have extensive mouth lesions and are drooling should be excluded until they can eat comfortably, get control of the drooling, and are well enough to participate in all program activities.
Follow the direction of your healthcare provider or occupational health at your workplace.
Note: Exclusion guidelines may differ for healthcare workers.
Contact our Communicable Disease Control (CDC) program at 705-474-1400 or toll free at 1-800-563-2808, ext. 5229, or by email to cdc@healthunit.ca for more information.
Last reviewed: Apr 2026, by CDC