Herpes simplex virus type 1 (HSV-1) causes cold sores, which are small blisters that usually form on the lips. Other symptoms may include fever and tiredness. HSV-1 is widespread and highly contagious.

A person may develop cold sores throughout their life because the virus remains in a person’s body permanently. The virus lies dormant in nerve cells and may become active again from time to time. When the virus is active, a cold sore may recur.

This article discusses the causes of cold sores, accompanying symptoms, and possible treatments.

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Herpes simplex virus (HSV) consists of two strains, type 1 (HSV-1) and type 2 (HSV-2). Type 1 is the most common. According to the World Health Organization (WHO), almost 3.7 million people under 50 have HSV-1, and 491 million have HSV-2.

The HSV-1 strain is more common partially due to how it spreads. HSV-1 can spread through mouth-to-mouth and mouth-to-genital contact.

When a person has a cold sore, they must wash their hands after applying cold sore cream or touching it as the infection can spread to other parts of the body.

The HSV-2 strain spreads through genital-to-genital contact during sex and causes genital herpes. HSV-1 also contributes to a few cases of genital herpes, for example, through oral sex.

In rare cases, HSV-2 transmission may occur during childbirth, resulting in a baby contracting the virus.

Learn why cold sores keep coming back.

According to the American Academy of Dermatology (AAD), most people with HSV-1 do not have any symptoms.

However, sometimes, painful cold sores develop around the mouth, typically on the lips. Many people know when they are getting a cold sore because they experience a burning or tingling sensation a couple of days before a cold sore erupts.

In rare cases, a sore can develop near the eye. This may spread to the eye and may cause sensitivity to light and pain. If this happens, a person should seek immediate medical attention.

People can have more than one sore. According to the AAD, cold sores usually break open within 48 hours, fluid will drain from the sore, and a yellow crust will develop.

Cold sores tend to last between 5–15 days. If a person has a cold sore that is taking longer to heal, they should speak with a healthcare professional.

Along with cold sores, other symptoms of an HSV-1 infection include:

Learn about the stages of a cold sore here.

A new HSV-1 infection may cause a cold sore, but some people may not present with any symptoms at all. HSV-1 is highly contagious, and most people experience it as a child. The symptoms usually go away within a couple of weeks.

There is currently no cure for HSV-1, and cold sores may occasionally recur throughout a person’s life.

HSV-1 lies dormant in a person’s nerve cells, and when they feel run down or fatigued or have a weakened immune system, the virus may become active again.

Additional triggers of recurring cold sores include:

  • stress
  • other infections, such as a cold or the flu
  • cuts around the mouth
  • dental treatment
  • cosmetic surgery
  • sunlight
  • hormonal changes, such as during menstruation

Learn about cold sores and babies here.

Cold sores are highly contagious.

HSV-1 spreads through contact with other sores, saliva, or other infected areas around the body. It usually transmits through mouth-to-mouth contact. This can be direct contact, such as kissing. Or, indirect contact, such as sharing cutlery or a towel with someone who has a cold sore.

The virus can even spread when no cold sores are present.

Learn how long a cold sore remains contagious.

Though HSV-1 is not technically a sexually transmitted infection (STI), it can spread through sexual contact. For example, a person receiving oral sex from someone with a cold sore may contract HSV-1 and develop genital herpes.

Learn more about STI’s here.

Cold sores typically go away without treatment within 2 weeks. There are no cures for cold sores, but people with severe symptoms may benefit from treatment.

Some over-the-counter (OTC) medications can help ease symptoms, such as anti-inflammatory and antiviral medicines.

In some cases, a doctor may prescribe antiviral medications, such as acyclovir or penciclovir. People with weakened immune systems take these medicines to prevent cold sores from worsening and spreading to other areas of the body.

If a cold sore is left untreated in people with compromised immune systems, serious complications, such as encephalitis, a type of brain infection, may occur.

People with cold sores should avoid oral contact with others until the sores have scabbed over. This will reduce the risk of the virus spreading to others.

Learn about cold sore medications here.

According to the ADA, some tips for treating cold sores at home include:

  • OTC pain killers and antivirals
  • applying ice or cold packs to the sores
  • avoiding spicy or acidic foods
  • placing a wet towel on the sores for 5–10 minutes
  • using petroleum jelly on the sores to prevent cracking

Learn about home remedies and other ways to get rid of a cold sore.

Most cases of cold sores will clear up on their own without a doctor. But symptoms lasting longer than 2 weeks may require medical attention.

People with certain conditions, such as dermatitis or those with underlying health conditions that weaken the immune system, should speak with a doctor if they experience persistent cold sores.

If anyone develops a cold sore near the eye, they should seek medical attention swiftly.

HSV-1 is a widespread and highly contagious virus that causes cold sores. Cold sores usually spread through mouth-to-mouth contact, but sharing cutlery can also aid transmission.

Cold sores can be painful and occur with other symptoms, such as fever. A cold sore typically appears with the first HSV-1 infection but may recur throughout a person’s life.

To prevent or reduce cold sores, it is beneficial to understand the triggers that cause them and avoid them wherever possible.

Most people can alleviate cold sore symptoms using OTC pain relievers and antiviral medicine.