Cold sores, also known as fever blisters, are a contagious viral infection caused by herpes simplex virus (HSV). they are characterized by inflamed, painful blisters on the lip or at the transition between the lip and skin. In most cases, infection with the herpes simplex virus occurs in the childhood due to direct contact (skin or saliva contact) for example mother-child contact. The virus hides in nerve cells for a lifetime and when it reactivated by certain triggers, it migrates from nerve cells back to the skin and multiplies there rapidly. Cold sores heal without treatment within 2-4 weeks. However, antiviral medication can help reduce the healing time.
Causes of Cold Sores
Cold sores are caused by herpes simplex virus (HSV) which is subdivided into type 1 (HSV-1) and type 2 (HSV-2). HSV-1 is the main cause of cold sores while HSV-2 mainly causes genital herpes (sexually transmitted disease). Cold sores are contagious and the virus can be transmitted by:
- Direct contact: the virus can be transmitted from one person to another by touching blisters or kissing a person with the active virus. Also, infected saliva can transmit the virus from one person to another.
- Droplet infection: the virus can also be transmitted over the air by droplet infection during coughing, sneezing, or speaking.
- Indirect infection: the virus can be transmitted via infected items such as glasses, napkins, and cutlery which are shared with an infected person. The virus can survive outside the body for up to 2 days.
During the initial infection, the virus enters the body via the skin or mucous membrane. Once infected with herpes simplex virus, the virus remains in the body for a lifetime. The genome (DNA) of the herpes simplex virus hides in the cell nucleus of nerve cells so that the immune system can’t recognize the virus DNA. Therefore, the immune system can’t fight it.
In nerve cells, the virus DNA can last for a lifetime in a state of rest. Certain triggers can reactivate the virus DNA leading to the migration of herpes virus from nerve cells back to the skin surface and multiplies there rapidly. On the skin surface, it causes an inflammatory reaction leading to cold sores.
Risk Factors of Cold Sores
Cold sores are caused by the herpes simplex virus that is reactivated from its resting state by some triggers such as:
- Fever and cold
- Mental stress such as stress, anxiety, and anger
- Sun exposure
- Dental treatment
- Hormonal changes during menstruation or pregnancy
- Immune deficiency such as HIV/AIDS
Symptoms of Cold Sores
Symptoms such as itching and tingling usually occur several days before the development of blisters. Cold sores always begin with:
- Tingling and itching.
- Stinging and burning.
- Redness of the affected site.
Then, blisters are formed on or around lips. Blisters are inflamed, painful, and filled with a fluid that contains a high concentration of herpes simplex viruses and is therefore very contagious. After several days, blisters may burst, creating shallow open sores, which after a few days crust over. Then, crusts gradually decrease leaving behind a new healthy skin. The healing of cold sores usually occurs within 2-4 weeks.
Some people may experience one or more of the following symptoms during the outbreak of cold sores:
- Swollen lymph nodes
- Muscle aches
Complication of Cold Sores
In rare cases, the herpes simplex virus (HSV-1) may spread to other parts of the body and causes serious problems, including:
- Herpetic whitlow: the virus can spread to fingers or thumbs leading to pain and swelling of the finger. It often occurs in thumb-sucking children with cold sores.
- Herpetic keratoconjunctivitis: the spread of herpes virus to eyes especially the cornea can cause corneal scars and corneal opacity leading to visual disorders up to blindness.
- Genital herpes: this infection is usually caused by the herpes simplex virus type 2 (HSV-2) or the herpes simplex virus type 1 (HSV-1). Oral herpes (HSV-1) can spread to genitals through oral sex.
- Herpesviral encephalitis: the herpes simplex virus can also affect the brain causing encephalitis, is an inflammation of the brain.
When to See a Doctor?
Cold sores usually don’t require a doctor visit. Call the doctor if you have:
- Persistent or severe cold sores
- High or persistent fever
- Difficulty swallowing
- Redness or irritation of eyes
- Weakened immune system
You should call your doctor immediately if you have these symptoms to prevent any complications.
Diagnosis of Cold Sores
The diagnosis is mainly based on the usual appearance of cold sores. To confirm the diagnosis your doctor may collect a swab of blister fluid for:
- Viral culture
- Polymerase chain reaction (PCR) to detect the herpes DNA.
Treatment of Cold Sores
Cold sores heal without treatment within 2-4 weeks. However, the treatment may be used to reduce the frequency and duration of outbreaks and relieve the pain. In order to reduce the healing time of cold sores, some antiviral agents may be used to target herpes simplex virus such as:
These active ingredients can be administered topically (creams and ointments) or orally (tablets). It is usually sufficient to apply an antiviral cream or ointment on the infected site several times a day. In severe cases, the doctor may inject an antiviral drug into a vein (intravenous administration). Also, the doctor may prescribe:
- Local anesthetic such as lidocaine or benzocaine to relieve the pain.
- Analgesics such as paracetamol or ibuprofen to relieve the pain and reduce the fever.
None of these treatments can completely eliminate the cause of cold sores. Because the herpes simplex virus remains in nerve cells for a lifetime and can break again at any time.
Prevention of Cold Sores
You can’t prevent cold sore outbreaks if you are infected with the causative virus (HSV). However, you can reduce the frequency of outbreaks by:
- Avoid prolonged exposure to sunlight and use sunblock.
- Try to avoid stress.
- Eat a well-balanced diet.
- Visit your doctor if you develop cold sores frequently. he/she may prescribe an antiviral medication on a regular basis.
Cold sores are contagious. To prevent the transmission of the herpes simplex virus (HSV) from one person to another or from the lip to other parts of the body, you should follow these precautions:
- Avoid direct contact with the virus: avoid close contact (such as kissing) with people who have fever blisters. The fluid on blisters contains a high concentration of HSV.
- Avoid sharing items: the virus can be transmitted from one person to another via infected items such as towels, razors, and glasses.
- Wash your hands: don’t touch the infected site and wash your hands to prevent the transmission of the virus to other people or to other parts of the body such as eyes.