Fever blister is the common name of an infection called oral herpes or herpes labialis. It is caused by infection of the lips, mouth and gums by herpes simplex type 1 virus (HSV-1). The genital herpes causing herpes simplex type 2 virus (HSV-2) can also sometimes result in oral herpes after an oral sex.
Blister formation is only one of the presentations of oral herpes and the symptoms of the oral infection with HSV-1 are highly variable. Many adults may be totally asymptomatic despite having the infection.
Symptoms first appear nearly 1 week after the exposure to the infection. The most common symptoms to appear are fever, headache, nausea and vomiting, sore throat, etc. These symptoms appear before the appearance of characteristic blisters on the lips. Blister formation occurs only in a fraction of cases, and the virus may go in dormant state after the initial mild illness without any blister formation.
Blisters most commonly occur at the border of the lip. Formation of blister is often preceded by tingling, burning or itching sensation around the lips for 24-48 hours, after which tiny, clear-fluid filled vesicles appear. The blisters later burst and form painful sores. These sores progress to form a crusted lesion. These cold sores usually heal completely in 7-10 days.
Without any treatment, the symptoms of fever blister resolve spontaneously within 1-2 weeks. Antiviral medications (like acyclovir, famciclovir, etc.) can shorten the duration of illness and reduce the severity of the symptoms. Ideally, for maximum efficacy, these medicines should be taken before the appearance of blisters.
Other than antiviral medications, certain home remedies can help in symptomatic relief by reducing the severity of the symptoms. Some of these practices are:
As already mentioned, untreated fever blister usually resolve in 1-2 weeks. Fever blister can occur again as the infection persists in the dormant, asymptomatic state and can flare up again anytime.
Conditions associated with depressed functioning of the immune system like AIDS, transplantation, anti-cancer medications, pregnancy, prolonged uncontrolled diabetes mellitus, stress, etc. can result in the flare up of a dormant infection. These conditions can also result in more severe presentation of the fever blister.
Fever blister occurring near the eye can result in spread of infection to eye, which can result in blindness by causing scarring of the cornea. A fever blister occurring near eye needs immediate medical attention.
Frequent touching of the oral herpes lesion can result in spread of herpes infection to fingers, a condition known as herpetic whitlow. Very rarely, the infection may spread to brain, resulting in encephalitis.
The infection usually spreads from person to person by direct contact (like touching, kissing, etc.) or sharing utensils like cups, spoons, straws, etc. Hence, these should be avoided.
Use of moisturizers to prevent drying of lips and avoiding sun (or using sunblock) may also help in preventing eruption of blisters after exposure to infection.