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Cold sores - symptoms, diagnosis, treatment and prevention

What are cold sores?

Cold sores are common and painful blisters around the lips and mouth caused by the herpes simplex virus.

The blisters will eventually break and ooze before crusting over and clearing up on their own after around seven to 10 days.

The sores are contagious until they are completely healed.

Around 7 in 10 people carry the cold sore virus, but many won't know they have it because it may not cause any symptoms.

Cold sore complications

Some children who are affected may become seriously ill. After the first infection, many people develop antibodies and never have another cold sore.

Although cold sores are generally not serious, the infection may be life-threatening for anyone who has HIV infection or has AIDS or whose immune system is suppressed by other disorders or medications.

The infection from a cold sore may cause blindness if it spreads to the eye and meningitis or encephalitis if it spreads to the brain.

What causes cold sores?

Cold sores are usually caused by the herpes simplex virus (HSV), which is transmitted by such forms of contact as kissing an infected person. Both types of HSV – type 1 and type 2 – can cause cold sores. A person with a cold sore who performs oral sex on another person can give that person genital herpes, and similarly genital herpes lesions can be spread to the lips causing cold sores.

Sores may develop as late as 20 days after exposure to the virus. Once the virus enters your body, it may emerge years later at or near the original site of entry. About two days before an attack you may experience itching or sensitivity at the site. The virus may be triggered by certain foods, stress, fever, colds, allergies, sunburn and menstruation.

What are the symptoms of cold sores?

  • Fluid-filled blisters or red, painful sores on or near the mouth.
  • Swollen, sensitive gums of a deep red colour.
  • A fever, flu-like symptoms and swollen lymph nodes in the neck often accompanying the first attack.
  • Tingling and itching in the area of a previous outbreak may be symptoms of a recurrence.

Seek medical advice about cold sores if:

  • You develop a high fever and/or chills; high fevers can be dangerous.
  • Your sores are very painful; you may be able to get prescription relief.
  • You have early signs of infection. Antiviral agents may shorten the course of illness only if started early. You can buy anti-viral cream such as aciclovir from the pharmacy, or your doctor may give you a prescription for cream or tablets.

How are cold sores diagnosed?

To see if you have the virus, your doctor may simply examine the cold sore or may take a swab from it to be tested in the laboratory. Rarely your doctor may also test your blood for antibodies to the herpes simplex virus (HSV). A positive antibody test only proves that you have the virus, but does not indicate whether or not the virus is active or when you may have acquired it.

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