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Cold Sores


Cold sores are a common viral infection, also known as fever blisters. The medical terminology for this disease is herpes labialis. They appear as a small cluster of fluid-filled blisters or sores that surround the lip region primarily. This condition is contagious and can spread when a person comes into contact with a cold sore or contaminated fluid of an infected person, such as sharing eating utensils or razors, kissing an infected person, or touching that person's saliva. Cold sores can occur inside the mouth and mucous membranes lining our tongue, lips, and cheeks. In such cases, it is known as herpetic stomatitis. They persist for almost two weeks while many patients remain asymptomatic despite having the virus in their systems.

Risk Factors and Epidemiology

Once a person has been tested positive for the herpes simplex virus, multiple factors can cause the reactivation of the virus that results in cold sores. One of the most common risk factors is fever. Any underlying bacterial, viral, or fungal infection that causes fever and decreases immunity can activate the herpes simplex virus. Other diseases that compromise the immune system, such as HIV, cancer, lupus, etc., are major risk factors. Changes in hormonal levels during menstruation or stress can also contribute to the activation of the virus. If you have undergone any recent lip or dental surgery, you might also be at risk. The most common way of its spread is through coming in direct contact with the site of blisters. Therefore kissing, sharing toothbrushes, or using razors with an infected person is a critical risk factor.

Also, you are at risk if you have a weakened immune system as a result of the following conditions and treatments:

  • Atopic dermatitis
  • Had chemotherapies for cancer
  • Used anti-rejection medications for Organ transplant

Generally, research has estimated that almost 66% of the global population have herpes simplex virus 1 in their bodies. It remains inactive inside our system unless reactivated by any causes mentioned above.


The primary cause of cold sores is Herpes Simplex Virus 1 (HSV-1). Herpes Simplex Virus 2 (HSV-2) might be the causative agent in some cases. The virus enters the body by coming in contact with mucous membrane lining or any break in the skin around the mouth. Close contact, such as kissing or oral sex, can spread either type to the face or genitals. After its entrance, it remains dormant inside the body for a long period. When it reactivates, it travels along with the nervous supply to the lips and oral cavity and forms fluid-filled blisters that persist for a week or two. Common causes that trigger the activation of the herpes simplex virus include fever, infectious diseases, menstruation, stress, dehydration, sunburn, traumatic injury, botox, lip tattooing, and any other surgical or dental procedure. 


The diagnosis of cold sores is mainly made by reviewing the history and examining the blisters. For conformational diagnosis, your doctor might recommend a swab test taken from a sample of the fluid in blisters to confirm the presence of the herpes simplex virus.

Signs And Symptoms

The symptoms of cold sores appear in stages as the virus progresses along with the nerve supply to lips and the oral cavity. Once the virus is reactivated, you might experience a burning or tingling sensation on or around your lips even before blisters appear. After a day or two, small clusters of fluid-filled blisters appear along the affected region. Eventually, the fluid drains out, and the blisters become painful sores. This is the most irritable stage, and the patient might have minor to extreme difficulty during eating and drinking. The sores dry out within 4-5 days, forming a crust. A few days later, new skin forms underneath the region of sores, the dried crust falls off, and the healing process is completed. In a few cases, fever, sore throat, headache, malaise, and swollen lymph nodes might be present, along with other symptoms. 


The primary treatment of cold sores is symptomatic because your immune system naturally fights off the virus in 10-14 days. Antiviral ointments such as penciclovir can be applied to the blisters to reduce the symptoms. A topical anesthetic agent such a lignocaine can effectively numb the pain of these sores. Antiseptic mouthwashes containing ethanol can be effective as well. Extremely hot or spicy food should be avoided during the healing period of this infection.


Antiviral drugs such as acyclovir, valacyclovir, penciclovir, and famciclovir are prescribed to reduce the symptoms of cold sores and speed up the healing process. Your doctor might prescribe these medicines if either the sores are occurring for the first time or when they are painful beyond tolerance. In most cold sores caused by herpes simplex virus 1, the healing process does not require any medication and completes within 2-14 days.

Differential Diagnosis

Cold sores can be confused with another type of oral ulcer, especially cranky sores (aphthous ulcers). Other diseases that mimic the symptoms of cold sores include oral candidiasis, stomatitis, pharyngitis, folliculitis, angular cheilitis, Behcet’s syndrome, Steven Johnson’s syndrome, and hand, foot, and mouth disease.  


To this time, there is no vaccine or permanent cure for cold sores. Once the virus has entered your body, it can remain inside a dormant stage for a lifetime. The only care that can be done is to manage the risk factors and use the prescribed medication or ointments in case of symptoms.


The primary prevention for cold sores is to avoid direct contact with a person having an active viral infection. As a general rule, kissing or sharing a toothbrush, razor, etc., with an infected person must be avoided. If you have already been diagnosed with HSV-1 infection before, managing all the risk factors mentioned above is necessary to lessen the chance of occurrence. Patients undergoing chemotherapy or radiotherapy should use the required preventive measures guided by their healthcare providers. Similarly, patients with immunocompromising diseases such as HIV, lupus, etc., should follow the same guidelines. Antiviral drugs such as acyclovir or famciclovir can reduce the recurrence of cold sores if they’re taken before the formation of blisters. If stress triggers the virus, you should employ stress management techniques to facilitate its replication. Learning and managing the trigger factors of the herpes simplex virus is the most effective way to prevent the appearance of cold sores.

Our clinical experts continually monitor the health and medical content posted on CURA4U, and we update our blogs and articles when new information becomes available. Last reviewed by Dr.Saad Zia on May 15, 2023. 



Cold sores - NHS (www.nhs.uk)


Cold sores: Diagnosis and treatment (aad.org)


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