What Are the Common Causes of Cold Sores?

Amanda R. Bell
Amanda R. Bell
Cold sores are often spread through kissing.
Cold sores are often spread through kissing.

The most common causes of cold sores are herpes simplex virus one (HSV-1) and herpes simplex virus two (HSV-2) which in some cases are known as human herpes viruses one and two. These viruses can be passed among people through physical contact with an active lesion. Once the virus is in a person’s system, an outbreak can occur due to illness, environmental irritants, emotional distress, and other issues. Once the virus is contracted, there is no way to prevent a cold sore outbreak.

Cold sores are caused by a common virus, herpes simplex 1.
Cold sores are caused by a common virus, herpes simplex 1.

HSV-1 is one of the most common causes of cold sores and can produce lesions, also known as fever blisters, on and in the mouth as well as inside the nose or on the face. HSV-2 is primarily responsible for genital herpes, although it can also cause cold sores. These viruses are extremely contagious; they can be transferred both during an outbreak and, in rare cases, when the virus is considered dormant.

The viruses are primarily passed from a person with an active lesion via kissing or oral contact with the genitals of a person with HSV-1 or HSV-2. When an active lesion is inside of the mouth or nose, a person’s saliva or mucus can carry the active virus and transfer it to someone else. Sharing a toothbrush, drink, or other items that come in contact with the viruses are common causes of cold sores.

In rare cases, the skin surrounding an active lesion can also shed the virus. The majority of cold sore cases are developed at a young age, often by a child receiving an innocent kiss from an adult. Once the virus is transferred, it lays dormant in the body until triggered. In some instances, the virus may remain dormant for a person’s entire life and never produce a cold sore.

Several different factors can trigger HSV-1 or HSV-2 into producing a lesion. The most common trigger is a moderate to high fever, cold, or other minor illness. In some cases, prolonged sun exposure or very cold weather can activate the virus. High emotional levels, especially stress and exhaustion, can also result in an outbreak.

Changes in hormones are also common causes of cold sores. In women, menstruation, pregnancy, or breastfeeding can cause the herpes simplex virus to activate. Men who experience a decrease in testosterone, often later in life, or other hormonal changes may also experience an increase in cold sores. Certain foods, drinks, and even prescription medications can also cause a reaction in those carrying HSV-1 or HSV-2; while these are not typically causes of cold sores, they can either bring on an outbreak or irritate an existing one. While these things can trigger the causes of cold sores, several other unknown factors may play a part. While there is no way to prevent them, steps can be taken to avoid transmitting the viruses, and over-the-counter and prescription topical agents can help a cold sore heal more quickly.

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Discussion Comments


Most of us know that herpes type 2 (the sexually transmitted one) also causes cold sores on the lips. But did you know that cold sores caused by herpes type 1 can spread to the genital area during oral sex?


@ddljohn-- There can be different triggers for cold sores and cold weather and chapped lips are definitely triggers.

I tend to get cold sores whenever I have a fever and sometimes I get it during my menstrual period. My sister gets cold sores when she's stressed. The poor thing is in college and is always breaking out at the end of the semester during exam time!

Who knows when we got the virus. It could have been at any point in our lives. We might have gotten it from parents, friends or people we dated. Drinking from someone else's water bottle is enough to get it. Some people think that we can only spread the virus when we have an active cold sore but that's not true. Our body shed the virus periodically, so it's possible to spread it at any time really.


I have a cold sore for the first time in my life. I'm not under a lot of stress and I'm not ill either, so I'm not sure why it happened. My lips were a little dry and cracked due to cold weather and the cold sore seems to have popped up where my lip was cracked. I guess my immune system is not as strong as I thought it was.

Since this is my first cold sore and I haven't had close contact with anyone recently, I guess I had gotten the virus a long time ago. It was dormant up until now. I just hope I don't get another one anytime soon because I hate it. I can't believe how much pain a little blister can cause.

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    • Cold sores are often spread through kissing.
      Cold sores are often spread through kissing.
    • Cold sores are caused by a common virus, herpes simplex 1.
      Cold sores are caused by a common virus, herpes simplex 1.