A risk factor is something that increases your likelihood of getting a disease or condition.
It is possible to develop cold sores with or without the risk factors listed below. However, the more risk factors you have, the greater your likelihood of developing cold sores.
The viruses that cause cold sores are easily spread. They come out of the skin and are “shed” from the site of the cold sore for 1-2 days before the sore appears. Then the virus is in the fluid of the cold sore blisters.
Once you have a herpes simplex infection, cold sores often form because of stress or illness. Some may form without an identifiable trigger.
Herpes simplex virus type 1 (HSV-1) can be spread by close contact with someone who has a cold sore. It can also be spread through personal items that are contaminated with the virus such as razors, towels, or eating utensils. Kissing or sharing personal items with a person who has a cold sore will increase your risk of getting HSV-1. The virus can also be spread to the genital area during oral sex. People with cold sores should not perform oral sex on their partners. The virus can be spread even when no cold sores are present.
Infants and young children up to 3 years old have an increased risk of being exposed to HSV-1.
Exposure to sunlight or other ultraviolet light is a common trigger for cold sores.
Stress on the body due to illness or excessive exercise can weaken the body’s immune system. This can lead to an outbreak of cold sores. Common examples of stress or illness include:
Infection, fever, or
coldPhysical injuryDental surgeryMenstruation
Medications and/or health conditions that suppress the immune system
Cold sore outbreaks commonly occur during times of emotional stress. The type of stress that activates cold sores is typically negative stress, instead of stress due to positive or normal life-changing events.
Herpes causes & risk factors. American Academy of Family Physicians Family Doctor website. Available at:
http://familydoctor.org/familydoctor/en/diseases-conditions/herpes/causes-risk-factors.html. Updated December 2010. Accessed February 14, 2014.
Herpes simplex. DermNet NZ website. Available at:
http://dermnetnz.org/viral/herpes-simplex.html. Updated February 6, 2013. Accessed February 14, 2014.
Kuehl B. Cold sores: how to prevent and treat them. Skin Care Guide website. Available at:
http://www.skincareguide.ca/articles/herpes/to_prevent_cold_sores.html. Accessed February 14, 2014.
Oral herpes. EBSCO DynaMed website. Available at:
http://www.ebscohost.com/dynamed. Updated January 30, 2014. Accessed February 14, 2014.
Last reviewed February 2016 by David L. Horn, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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