Fever, infections (particularly bronchitis and pneumonia), stress, excessive exposure to sunlight or even menstruation can sometimes lead to the appearance of “fever blisters” or “cold sores”. These are multiple, transparent blisters grouped together — filled with a clear fluid — that are situated near the margins of the lips, the nose or the cheeks. They appear without warning and disappear in much the same way in around two weeks.

These lesions are due to infection by one of the Herpes group of viruses. The various members of the Herpes family that can cause infections such as chicken pox, herpes zoster and an STD (sexually transmitted disease). The one causing the fever blister is usually the Herpes Simplex Virus (HSV) type 1 but can also be type 2.

Exposure to the virus starts from birth. The rate of infection increases from 0 per cent at birth to 30 per cent by age 30, 50 per cent by age 50 and 90 per cent by the age of 70. Exposure does not necessarily result in blisters. The virus is capable of remaining dormant till the immune system is sufficiently weakened for it to manifest.

There is tingling and mild discomfort 2-3 days before the lesions erupt. Children (under five years) may have fever, headache, dizziness and nausea. Although the blisters have not yet appeared, the person can still spread the infection. Soon, the affected area becomes a mild red. Tiny, pimple-like swellings filled with a clear fluid erupt. These usually appear in clusters on the lip itself, the border of the lips, the chin or nose. The blisters then burst and release a clear fluid. This fluid is highly contagious. The blisters then crust over and form scabs, which fall off. The scabs too contain potentially infective viruses.

In children (under five) the infection may start in the mouth. Initially there is redness, followed by the appearance of multiple blisters. These rapidly break down and can coalesce, forming multiple painful shallow ulcers. Swallowing becomes painful so the child may refuse to eat or drink. It may be difficult to even swallow saliva. As a result the child drools. The neck may be swollen with enlarged and painful lymph nodes.

The unfortunate reality is that the virus never entirely leaves the body once it enters. It establishes permanent residence in one of the branches of the trigeminal nerve, which supplies various areas of the face.

In 20 per cent of the people, the virus remains latent in the body and does not resurface. In the majority there are one to three recurrences in a year. Some unfortunate individuals have up to 12 attacks a year.

The cold sores usually clear up by themselves within two weeks if left alone. A doctor needs to be consulted if the lesions are still present after a couple of weeks. This may occur if the initial diagnosis is not be correct or secondary infection has occurred.

Treatment is most effective if started in the early stages when the tingling occurs but the blisters have not yet appeared. Unless people have frequent attacks, they do not realise that this is the prelude to an attack.

Applying creams containing one per cent lemon extract, zinc oxide or the anti viral “cyclovir” group of compounds twice or thrice a day will reduce the symptoms, and speed healing by a day or two. In young children, people with deficient immunity and the elderly, doctors may start anti-viral tablets to speed up the healing process.

Cold sores are highly infectious. They are also itchy, pricking and irritating. It is difficult to not touch, scratch or pick at the scabs once they form. The virus then transfers to the hands and gets deposited on any surface it comes into contact with. It survives on tables, walls or clothes for many weeks. The virus can also be transferred through utensils or shared food. Any person who touches these contaminated surfaces and then their face, nose, lips or mouth can develop the infection. Children who place their infected fingers in their mouth develop infection there. It can also be transferred from feeding bottles, pacifiers and toys. Any blisters which recur days, months or years later are equally infectious.

One of the best ways to prevent infection is not to touch the infected area, to wash hands frequently, and not share utensils or food. Once the primary infection has occurred, it is difficult to predict or prevent recurrences.

Dr Gita Mathai is a paediatrician with a family practice at Vellore. Questions on health issues may be emailed to her at yourhealthgm@yahoo.co.in