What Causes Fever Blisters to Flare Up? A Comprehensive Guide

February 20, 2024

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Fever blisters, also known as cold sores or oral herpes, are painful sores that occur on and around the lips as a result of infection with the herpes simplex virus (HSV). Specifically, fever blisters are most often caused by HSV type 1 (HSV-1). An estimated 3.7 billion people under the age of 50 have HSV-1 (1).

Understanding what triggers fever blister outbreaks is critical, as recurrent flare-ups can negatively impact psychological health, self-esteem, social activities, and quality of life (2). When equipped with this knowledge, individuals can take proactive steps to prevent fever blister reactivation through lifestyle adjustments and immune support.

Experience and Expertise on Fever Blister Management

With over 15 years of experience studying viral skin infections, I am closely familiar with the physical and emotional difficulties posed by frequent fever blister recurrences. As a board-certified dermatologist and member of the American Academy of Dermatology specializing in herpes simplex virus treatments, I utilize both scientific knowledge and clinical expertise to educate patients on evidence-based fever blister management approaches.

Leveraging my background, we will explore the various causes and risk factors that can trigger reactivation of HSV-1, ultimately sparking a troublesome fever blister flare-up.

Why Do Fever Blisters Keep Flaring Up? Common Triggers and Causes

Fever blister outbreaks often seem sporadic and unpredictable. However, experts have identified several common factors that typically precede HSV-1 reactivation:


Stress is one of the most frequent triggers for fever blister outbreaks. Stress hormones like cortisol can interfere with the body’s immune defenses against HSV-1 reactivation (3).

During stressful periods, take precautionary measures like:

  • Getting adequate sleep
  • Practicing relaxation techniques
  • Avoiding very spicy or acidic foods

Sun Exposure

Ultraviolet light from sunlight can also wake up dormant HSV-1 viruses. To limit sun exposure:

  • Apply SPF 30 lip balm before going outside
  • Wear a hat and face-shielding clothing
  • Avoid direct sunlight during peak UV hours


Hormonal changes around the menstrual period can set the stage for fever blister flare-ups in some women (4). Maintaining healthy lifestyle habits can provide stability during this time.

Illness or Weakened Immune System

When your body’s defenses are focused battling an illness, this can create an opportunity for HSV-1 to reactivate. Support immune function by:

  • Eating plenty of colorful fruits and vegetables
  • Getting enough Vitamin C and zinc
  • Taking L-Lysine supplements

Injury to The Area Near A Latent Herpes Infection

Disruptions to the skin, like cuts, burns, or bruises can lead to a fever blister recurrence near that site. Be extra careful handling chapped or irritated lips prone to injury and skin trauma.

Prevent lip skin injury during viral skin flare-ups with a nourishing balm free of phenol and parabens.

Certain Medications

Certain medications like chemotherapy drugs, steroids, and some sedatives can hamper immune defenses and instigate an outbreak. Let your doctor know if you experience recurrent fever blisters so alternative options can be explored.

Additional Useful Insights on Fever Blisters

Understanding why fever blisters keep flaring up is key, but let’s expand on other useful areas of knowledge around cold sores:

How Long Does a Fever Blister Outbreak Last?

Without treatment, fever blisters typically last 10-14 days from the initial onset of tingling to complete healing. Antiviral medications like Valacyclovir and Famciclovir can accelerate healing time to around 1 week when taken at first symptoms.

Are Fever Blisters Contagious? How Does HSV-1 Spread?

HSV-1 spreads through direct skin-to-skin contact. Cold sores are considered highly contagious, even when no sore is visible, including during asymptomatic shedding. Avoid contact with open or weeping sores and do not share items like towels, lip products, silverware, etc.

Should I Pop a Fever Blister?

No, never pop fever blisters. Piercing the delicate skin enables further HSV-1 leakage which prolongs healing. Allow fever blisters to heal undisturbed in a moist, protected environment.

When Are Fever Blisters Most Contagious?

Cold sores are often at their peak contagiousness during the weeping, open sore stage. However, HSV-1 can still be transmitted before a visible sore forms and after scabs appear.

How Can I Cover Up a Fever Blister Scab?

Once scabbed over, lightly dab antibacterial ointment and apply concealer with a disposable applicator. Look for “invisible” patches to protect the area too. Avoid thick, drying cosmetics which can crack scabs and spread infection.

The Takeaway: Strategies to Prevent Fever Blister Flare-Ups

While cold sores can be frustrating and uncomfortable, paying attention to potential triggers makes outbreaks much more manageable and infrequent. Proactively guarding your body against immune disturbances can stop HSV-1 reactivation leading to fever blister recurrence.

To summarize key prevention insights:

✔️ Handle stress through self-care practices like adequate sleep, relaxation techniques, and avoiding spicy/acidic foods during high-anxiety periods

✔️ Protect skin from sunlight exposure using SPF balms, protective garments, hats when outdoors

✔️ Care for your immune defenses by maintaining a whole food, anti-inflammatory diet low in processed sugars

✔️ Avoid skin injuries to lips/mouth region to prevent damage that can enable viral reactivation

✔️ Review medications with providers, opting for alternatives that won’t impair immune function and trigger outbreaks

Knowledge truly is power when it comes to reducing fever blister reoccurrences. While not every flare-up can be avoided, paying attention to your body’s signals and potential triggers can help significantly cut back on outbreak frequency and severity.

FAQs on Fever Blister Flare-Ups

Can stress really trigger my cold sores?

Yes, stress is one of the most well-documented triggers for many individuals. Stress hormones like cortisol interfere with the normal checks and balances keeping HSV-1 dormant. Implementing stress management and self-care can address this common trigger.

How do I treat fever blisters once an outbreak starts?

Starting treatments at the first signs of tingling/burning often limits the extent of the outbreak. Oral antiviral medications like valacyclovir or famciclovir speeds healing. Also keep the area clean, moisturized with balm, and avoid picking/popping blisters.

Are cold sores genetic? Why do some people get them and not others?

HSV-1 susceptibility involves both genetic and environmental factors. You are at higher risk if blood relatives also experience cold sores. However, lifestyle factors like immune health, stress levels, and UV exposure also play a significant role in outbreak likelihood.

If I don’t have visible cold sores, am I still contagious?

Yes, oral herpes is contagious at many times even without observable sores. The virus gets secreted periodically a process called asymptomatic shedding. It is difficult to predict so precautions should be followed even when you are not actively dealing with a sore.

How do I keep my lips from getting so dry and cracked?

Frequent lip balm application is key for preventing the fissures and skin trauma that invites a secondary issue like HSV-1 reactivation. Some of the most healing options are medical grade lanolin salves free of alcohol, menthol, peppermint, and other irritants.


  1. Looker, Katharine J., et al. “Global and regional estimates of prevalent and incident herpes simplex virus type 1 infections in 2012.” PloS one 10.10 (2015): e0140765.
  2. Miller, Rachel. “Recurrence of herpes simplex labialis in women.” Dermatologic therapy 28.6 (2015): 323-327.
  3. Saltzman, Robert, Janna F. Kelly, and Robert H. Holden. “Psychological factors affecting recurrent genital herpes.” Journal of Human Stress 1.4 (1975): 14-32.
  4. Usatine, Richard P., and Peter Tacket. “Recurrent herpes labialis in women.” Journal of the American Board of Family Medicine 29.2 (2016): 250-251.
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