Fever blisters, also known as cold sores, are small painful blisters that develop on the lips or around the mouth. They are caused by the herpes simplex virus (HSV). There are two types of HSV that can cause cold sores: HSV-1 and HSV-2. HSV-1 is the most common cause of cold sores and is typically transmitted in childhood through contact with infected saliva. Once a person is infected with HSV-1, the virus stays dormant in the body and can reactivate throughout life, leading to recurrent cold sores.
What causes fever blisters?
Fever blisters are caused by infection with the herpes simplex virus (HSV). There are two types of HSV:
- HSV-1 – This is the most common cause of cold sores. HSV-1 is transmitted through contact with infected saliva and usually causes sores around the mouth.
- HSV-2 – This type is more often associated with genital herpes. However, HSV-2 can also cause oral cold sores in some cases.
Once a person is infected with HSV, the virus never fully leaves the body. It resides inactive in nerve cells and can reactivate periodically. When reactivated, the virus travels down nerve fibers to the skin and causes cold sores.
How do people get infected with HSV?
There are several ways HSV can be transmitted and cause a first infection:
- Oral contact – Kissing or sharing drinks/utensils with someone who has an active cold sore can transmit HSV-1.
- Skin contact – Touching active cold sores can spread HSV to other areas of the body, like the fingers.
- From mother to newborn – Pregnant women with an active genital HSV-2 outbreak can transmit the virus to their baby during childbirth.
Once infected, HSV establishes latency in nerve cells. Future cold sores are caused by reactivation of latent virus, not new exposure.
What triggers fever blisters to recur?
There are several potential triggers that can cause dormant HSV to reactivate:
- Stress – Increased stress hormones may reactivate HSV.
- Fatigue – Physical or emotional exhaustion may activate the virus.
- Fever/illness – A compromised immune system makes reactivation more likely.
- Menstruation – Hormonal changes may contribute to recurrence in some women.
- Sun exposure – UV light has been shown to stimulate reactivation.
- Skin trauma – Things like sunburn, windburn, or chapped lips can trigger outbreaks.
The exact trigger often can’t be identified. Reactivation results from complex interactions between the virus and the immune system.
Who is at risk for recurring fever blisters?
Anyone who has been infected with HSV is at risk for recurrent fever blisters. However, some people are more prone to frequent outbreaks. Risk factors include:
- Having an initial HSV infection at a young age
- Experiencing frequent or severe first outbreaks
- Having a weakened immune system
- Increased exposure to triggers like sunlight or stress
- Hormonal changes, like those during menstruation
- Having another illness like a cold or flu
Why do fever blisters keep recurring?
Fever blisters recur because HSV establishes life-long latency in nerve cells. Even after the initial infection is cleared, some virus remains in a dormant state inside cells. Over time, various triggers can reactivate these viruses, causing a recurrent outbreak. Recurrence is the nature of all herpes infections.
The reasons fever blisters keep recurring include:
- HSV latency allows the virus to persist in the body indefinitely.
- Reactivation triggers are often unavoidable day-to-day stresses.
- Aging immune systems may have more trouble keeping latent virus suppressed.
- Reactivated virus travels down nerve fibers where it is protected from immune detection.
Currently, there is no cure that can fully eliminate latent HSV from the body. Periodic reactivation may occur throughout life.
How often do fever blister outbreaks occur?
The frequency of fever blister outbreaks varies greatly from person to person. Some people experience outbreaks several times per year, while others rarely have recurrences. On average, those with HSV-1 tend to have more frequent outbreaks than those with HSV-2.
In the first year after initial infection, some people may have multiple outbreaks. Over time, recurrences often become less frequent. The following table provides an overview of the typical recurrence patterns:
|Time since initial infection
|Average # of outbreaks per year
|5 or more
|1 – 5 years
|1 – 3
|Over 5 years
However, the number of outbreaks can still be highly variable from person to person regardless of the time since initial infection.
How long do fever blister outbreaks last?
A typical cold sore outbreak lasts 7-10 days from the first signs of tingling/itching until complete healing. The blisters usually crust and scab within 4-5 days. The timeline of a fever blister outbreak consists of:
- Prodrome – 1-2 days of tingling, itching, or burning at the infection site
- Blister formation – Small clustered blisters develop over 2-3 days
- Peak symptoms – Blisters become full and swollen for 2-3 days
- Crusting/scabbing – 4-5 days for blisters to dry out and begin healing
- Healing – Scabs disappear after 7-10 days
Outbreaks caused by HSV-1 tend to last slightly longer than HSV-2 outbreaks. Individual outbreak duration can also vary.
Can fever blisters appear without other symptoms?
Yes, it’s possible to develop cold sore lesions without prodromal symptoms. However, most outbreaks are preceded by early warning signs like itching, tingling, burning, or pain at the site where blisters will emerge. Skipping the prodrome phase is more common in people who have had HSV for many years.
Even without prodrome symptoms, typical fever blisters will still progress through the blister and crusting stages of an outbreak before healing. The overall sequence remains the same, but the early symptoms may be mild or absent.
Are fever blisters contagious when no sores are present?
No, fever blisters are only contagious when active sores are present. When dormant in nerve cells, HSV does not shed viral particles and cannot be spread. The only time the virus can be transmitted to others is during active replication, when it is released into the skin and oral secretions.
The most infectious period is when fever blisters are in the weeping/oozing stage, which occurs about 2-3 days after initial lesion formation. Maximum contagiousness coincides with peak viral shedding.
Can stress alone cause fever blisters?
Stress alone does not directly cause fever blisters. However, stress is frequently reported as a contributing trigger that can reactivate latent HSV and lead to an outbreak. During times of stress, immune function may be impaired, allowing the virus to come out of dormancy.
So while stress does not infect someone with HSV, ongoing stressors may activate virus already present in the body. Reducing stress through relaxation techniques may help decrease outbreak frequency in susceptible individuals.
In summary, fever blisters are caused by herpes simplex virus infections that recur intermittently throughout life. HSV establishes viral latency in nerve tissues, allowing periodic reactivation to occur in response to various triggers. There is currently no cure to eliminate latent virus from the body. However, antiviral medications can shorten outbreak duration and reduce frequency in many cases. Avoiding reactivation triggers like stress, illness, and sun exposure may also help decrease recurrences.