Cold sores are often associated with kissing and oral sex. The problem is that herpes simplex virus (HSV-1) can also be transferred from person to person for a variety of reasons, many of which are innocent. Due to this simple yet complex association, the truth can easily be concealed. Distrust and accusations of cheating may occur when your partner has a cold sore when you don’t.

What does a cold sore mean concerning your relationship? Who knows? Unfortunately, it might be up to you to do some investigating to find out the truth. This is especially true if your partner is not willing to talk openly about the issue for a reason that is unclear.

Noticing changes in your boyfriend or girlfriend’s behavior could play a huge role. Where they are and where they have been will likely provide more helpful answers than the actual blister. In order contract HSV-1, you have to engage in some form of contact with a person or an item.

In this post, you will learn about the importance of gathering evidence before making an accusation. You will also find out more about the potentially innocent ways HSV-1 can be transferred. Before you enter a verbal confrontation with your partner, it is essential to cover all of the possibilities. Cheating is horrible. However, accusing an honest person of cheating is slanderous.

Are Cold Sores Proof that Your Boyfriend (or Girlfriend) is a Cheat?

Potential proof? Yes. Definitive proof? No.

The HSV-1 transfer is often due to mouth-to-mouth kissing or oral sex. However, there is more to the story if you are attempting to use cold sores as proof that your partner is cheating. Using fever blisters as proof is not as cut and dry as it would seem.

If your partner has a cold sore, this is most likely proof of engagement. Not hard evidence of actual cheating. You can conclude that your partner has come in contact with an HSV-1 carrier…but who? The “who” is the million dollar question.

The real kicker can identify this mystery person. Unless you can determine that person, cold sores are not proof of cheating. At least not at face value.

To summarize:

  • If your boyfriend or girlfriend is in the midst of an outbreak, this does not mean they are cheating. At least regarding definitive proof that cannot be refuted. If you are concerned, you will have to dig deeper. The appearance of a blister is not concrete evidence of wrongdoing.
  • Kissing and oral sex are common ways that HSV-1 is transferred.[1] While that alone can signal cheating, it is not that simple. The timing of the outbreak can be critical as well as other factors.

Do You Have Additional Evidence that He (or She) is Cheating?

This part of the equation is critically important. If all you have is the visual of a blister on your partner’s lip, the verdict is inconclusive. It would also be potentially reckless to make a bold comment to your partner (about cheating) without evidence. The last thing you want to do is lose your relationship because you made a claim that was proven false.

If you have been in a relationship for several months or even years, then you likely know your partner’s habits. You probably know their routine. The better that you know them, the easier it will be to spot something unusual.

  • Example: Are they spending more time at work than usual? Are they claiming they have to work late many nights? Are they finding reasons not to spend time with you? Are they canceling dates and gatherings?

Red flags in behavior will likely carry more weight concerning “cheating evidence” than the cold sore itself. If the blister has come on the heels of some slightly mysterious behavior, then you might have a significant concern.

To recap:

  • Having additional evidence is critical. Not only to provide answers but to keep you from making a mistake. Are you willing to confront your partner and accuse them of cheating because of a blister? If you are proven wrong, you have potentially lost your entire relationship.
  • If you have been with your partner a long time, you likely know their behavior. You know their daily routine. You know their personality. Little changes in their day-to-day association with you could help. If a blister has developed on the heels of some rather odd behavior, that could be a sign of cheating. In fact, personality changes and avoidance are more of a warning sign than having a cold sore blister.

Has He (she) Had Cold Sores in the Past But Kept It Secret?

Timing is critical and the possibility of keeping fever blisters a secret is all about timing. What does it mean? Have they been cheating, contracted HSV-1, and are now attempting to hide the blister? This is information you need to figure out without being too verbally aggressive with your partner.

Do you have proof of a secretive cold sore? If you have found an OTC cold sore treatment[2] on their person or within the home, that is critical. If they have cold sore creams and gels and never told you, this could be a red flag. Why are they hiding essential fever blister treatments? This is a question that needs to be addressed.

Everyone wants to conceal their cold sore. That’s the purpose of fever blister patches. However, concealing a sore and attempting to keep it a secret are not the same. If your boyfriend or girlfriend is trying to hide their HSV-1 status, this could be a sign of cheating. This is more likely if they recently developed their first outbreak while in a relationship with you.

To summarize:

  • There is a big difference between covering an existing cold sore and keeping an outbreak a secret. If you stumble upon cold sore treatment products that could be another red flag if you were never informed by your partner.

What Could Have Caused Cold Sores?

While kissing and oral sex are the primary causes of cold sores, there are other factors to consider. These additional factors can potentially be proof that he or she is not cheating.

Once you explore the fact that HSV-1 transfer can be due to sharing of items[3], the picture becomes rather muddy. Is it possible your partner went out on the town with friends and contracted HSV-1 from a friend? Perhaps he or she shared a drink with a friend? Maybe a cigarette was shared? If your partner has a friend with HSV-1, the viral transfer could have taken place most innocently.

Another thing to consider is family.

  • Example: Does your partner have a little brother or sister who carries HSV-1? It is indeed within reason that your boyfriend or girlfriend contracted HSV-1 from a family member.

While there are signs to look for when it comes to cheating, there are ways to contact HSV-1 that involve innocent behaviors.

Does a cold sore mean that my boyfriend is a cheat?

This is all the more reason why you must make your case before you confront your partner. That cold sore on your boyfriend’s lip could be from his sweet little sister.

To recap:

  • While kissing and oral sex are the two most common ways that HSV-1 is transferred, more innocent ways do exist. The sharing of drinks and cigarettes can also promote viral transfer as well as interaction with family. Not every kiss has to be a passionate exchange with a mistress.
  • Regarding the bigger picture, this section is food for thought when making your case. If you think your partner is cheating it is important to consider all possibilities before you fly off the handle.

Do You Really Have Enough Evidence?

This is critical. The evidence factor can mean the difference between confronting a legitimate cheat and making a fool of yourself. Before you decide to address the situation, especially an accusation, gather the facts.

Place yourself in a bit of a role reversal. Would you want your boyfriend or girlfriend making untrue claims about you without proof? Before you express your concerns, it is vital to consider the ramifications of not only being right…but also being wrong.

Strange behavior coupled with unspoken treatment that has been newly discovered could be the kicker. At least enough to warrant a conversation. However, if a sore is all you have to go on, it is best to choose your actions wisely.

Another thing to consider is your relationship history? Do you really have one? If you have been dating your partner for a matter of weeks, the cold sore could be from a prior relationship. Some people find it hard to bring up the subject of cold sores in relationships.

These are all important things to consider as it relates to evidence. While it is always wise to confront a known cheater, making the wrong move could prove to be foolish. You might be the one left all alone after you accuse an honest person of cheating.

To summarize:

  • Although the “cold sore jury” does not live in a court of law, you need to gather evidence correctly if you truly value your relationship.
  • While talking about your partner’s cold sore is one thing, making a bold accusation is another. Choose your actions (and words) wisely.


While it is always paramount to confront a cheater once you have the facts, a confrontation that is based on a blister is a slippery slope. You shouldn’t base the entire notion of cheating on a cold sore.

Just like most things in life, it is critical to gather information before making a bold move. Logic suggests that if your partner is genuinely a cheater, you will not have trouble finding real evidence. Likely bulk evidence that does not involve a medical ailment.

It never hurts to have a little patience. Time often has a way of revealing the truth. Never be afraid to lean on the clock. If your partner is really cheating, they will not be able to hide it for long. Abreva might be able to cover their blister, but it will not be able to cover their tracks.


  2. Leung AKC, Barankin B. Herpes Labialis: An Update. Recent Pat Inflamm Allergy Drug Discov. 2017;11(2):107-113. doi: 10.2174/1872213X11666171003151717.