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    What causes cold sores?

    On this page
    1. Cold sores and the herpes simplex virus
    2. How can I catch herpes?
    3. Triggers for recurring cold sores
    4. Cold sore treatment
    5. Cold sores and genital herpes

    Reviewed by our clinical team

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    Cold sores are common and typically clear up on their own, but lets look into what causes them and how we can help ease the discomfort they can cause.

    Cold sores and the herpes simplex virus

    Herpes simplex is a type of herpes virus that can cause many conditions. Two of the most common ones are cold sores and genital herpes.

    The herpes simplex virus is highly contagious and spreads through skin-to-skin contact. There are two types, HSV-1 and HSV-2; both can cause cold sores and genital herpes. HSV-1 more commonly causes cold sores. Genital herpes is a sexually transmitted disease caused by infection with HSV-2, it was the most common cause of genital infection but HSV-1 has overtaken it

    How can I catch herpes?

    You can contract the herpes simplex virus in several different ways.

    The following activities can cause cold sores:

    • Kissing someone with a cold sore
    • Sharing lip products, utensils or cups with someone who has a cold sore
    • Giving oral sex to someone who has genital herpes

    The following activities can cause genital herpes:

    • Receiving oral sex from a person with a cold sore
    • Having sex with a person who has genital herpes (usually during an outbreak of symptoms)

    Because genital herpes causes blisters to form across the thighs, buttocks, genitals and anus it’s not always easy to avoid contact with the virus during sex, even if you’re using condoms. For this reason, it’s a good idea to avoid having sex with someone until their symptoms have passed and their blisters healed.

    Triggers for recurring cold sores

    If you do contract the herpes virus and develop a cold sore, it’s important to understand a few things. Firstly, it’s common to experience recurring outbreaks of symptoms, even after your initial cold sore has cleared up. This is because the herpes virus passes through the skin and travels up into the nerves, where it lies dormant for long periods. In reaction to certain triggers, the virus causes a recurrence of symptoms.

    Triggers for cold sores include:

    • Having another infection
    • Having a fever
    • Feeling very stressed or upset
    • Being very tired
    • Menstruation
    • Receiving an injury to the affected area
    • Strong sunlight

    If you do suffer from the recurring cold sores, the good news is that there are several types of treatment available.

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    Cold sore treatment

    The first time you develop a cold sore, you can cover the blister with a cold sore patch, or ease the discomfort with a numbing cream or gel.

    For recurring cold sores, try stocking up on some antiviral creams over the counter in a pharmacy or – in more severe cases – talking to your doctor about getting prescription antiviral tablets. You can also try wearing a lip balm that contains SPF if you find that strong sunlight is a particular trigger.

    It’s also worth noting that there are some distinct cold sore stages, and that familiarising yourself with these can help you prepare for an outbreak:

    1. The dormant virus is triggered by illness/stress/menstruation etc. The virus travels to the area of original infection e.g. the lip
    2. The skin in that area begins to tingle or itch
    3. A red bump appears and develops into a blister
    4. The blister dries into a scab and falls off

    At stage three, when you begin to feel a tingling or itching in the site of a previous cold sore, you can start applying antiviral cream to the affected area or – if you have a prescription – start taking antiviral tablets.

    While you have a blister on your lip you should avoid intimate contact with other people, as you could spread the virus to them.

    Cold sores and genital herpes

    As previously stated, the herpes virus doesn’t easily spread from one area of the body to another – so if you have a cold sore, you needn’t worry about waking up one morning with blisters on your genitals.

    However, you should try to avoid touching the blister and then touching other areas of your body, as this can transmit the virus. It’s also important to take precautions during sex if either you or your partner has the herpes simplex virus.

    If you have a cold sore, refrain from kissing and giving oral sex to your partner; if you are experiencing an outbreak of genital herpes, refrain from having sex entirely until your symptoms have cleared up.

    Despite the stigma that surrounds genital herpes, it’s also worth noting that it’s not a severe condition and can be easily managed with the right treatments.
    If you think you might have contracted genital herpes, talk to a doctor or visit a sexual health clinic.


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