Cold Sore Won't Heal? Why Your Lip Is Blistering and What to Do Next

A cold sore is common, uncomfortable, and usually harmless. But when a cold sore won't heal, keeps coming back, or looks worse than usual, it's natural to wonder what's going on.

Most cold sores clear up on their own within 7 to 14 days. If yours is lingering beyond that, growing larger, or becoming more painful, it may be time to take a closer look.

Here's what you need to know about why your lip may be blistering — and what medical steps to consider next.

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What Is a Cold Sore?

A cold sore (also called herpes labialis) is caused by the herpes simplex virus type 1 (HSV-1). Once you're exposed to the virus, it stays in your body for life. It can reactivate from time to time, especially during stress or illness.

Cold sores usually appear:

• On or around the lips
• As small fluid-filled blisters
• In clusters
• With tingling, burning, or itching before they appear

They typically crust over and heal within two weeks.

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Why Isn't Your Cold Sore Healing?

If your cold sore won't heal, several factors could be responsible.

1. Your Immune System Is Under Stress

Cold sores are more likely to flare — and last longer — when your immune system is weakened. Common triggers include:

• Emotional stress
• Lack of sleep
• Fever or illness
• Hormonal changes
• Sun exposure
• Physical exhaustion

If your body is busy fighting something else, it may take longer to control the virus.

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2. You Didn't Start Treatment Early

Antiviral medications work best when started at the first sign of tingling or burning (the "prodrome" phase).

If treatment is delayed until after blisters form, healing may take longer.

Over-the-counter creams can help symptoms, but prescription oral antivirals such as acyclovir, valacyclovir, or famciclovir are generally more effective for moderate to severe outbreaks.

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3. The Cold Sore Became Infected

Sometimes a cold sore can develop a secondary bacterial infection.

Signs this may be happening include:

• Increasing redness spreading beyond the sore
• Pus instead of clear fluid
• Worsening pain
• Swelling
• Fever

If this occurs, you may need prescription antibiotics in addition to antiviral treatment.

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4. It May Not Be a Cold Sore

Not every lip blister is a cold sore.

Other conditions that can look similar include:

• Canker sores (usually inside the mouth, not on the lip surface)
• Impetigo (a bacterial skin infection with honey-colored crusting)
• Contact dermatitis (reaction to lip products or toothpaste)
• Angular cheilitis (cracking at the corners of the mouth)
• Shingles (painful blisters, usually on one side of the face)

If your blister looks unusual, spreads rapidly, or doesn't follow the typical cold sore pattern, it's worth getting evaluated.

If you're unsure whether your symptoms match a cold sore or something else, you can use Ubie's free AI-powered Blistering Symptom Checker to help identify potential causes and determine whether medical attention is needed.

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5. You Have Frequent or Severe Recurrences

If you get:

• More than 5–6 outbreaks per year
• Very large or painful cold sores
• Sores that last longer than 2–3 weeks

You may benefit from daily suppressive antiviral therapy. This reduces both outbreak frequency and severity.

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6. An Underlying Medical Condition

Rarely, a cold sore that won't heal may signal an underlying issue, such as:

• A weakened immune system
• Diabetes
• HIV infection
• Use of immune-suppressing medications (like steroids or chemotherapy)

If cold sores are unusually severe, persistent, or accompanied by other symptoms like unexplained weight loss, frequent infections, or extreme fatigue, speak with a healthcare professional promptly.

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When to See a Doctor About a Cold Sore

Most cold sores don't require medical care. However, you should speak to a doctor if:

• The sore lasts longer than 2 weeks
• It is extremely painful
• You develop a high fever
• The sore spreads to your eyes
• You have vision changes
• You have difficulty swallowing
• You have a weakened immune system
• You experience frequent outbreaks

Cold sores near the eye are especially serious. HSV infection in the eye (herpes keratitis) can threaten vision and requires urgent treatment.

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Medical Treatment Options

If your cold sore isn't healing, your doctor may recommend:

Prescription Oral Antivirals

These reduce viral replication and speed healing:

• Acyclovir
• Valacyclovir
• Famciclovir

These are most effective when started early but can still help later in the outbreak.

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Topical Prescription Treatments

Some antiviral creams may shorten healing time if used correctly.

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Antibiotics (If Infected)

If bacteria have infected the blister, antibiotics may be necessary.

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Suppressive Therapy

For people with frequent outbreaks, daily antiviral medication can significantly reduce recurrence.

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What You Can Do at Home

While waiting for healing, you can:

• Apply a cold compress to reduce discomfort
• Use lip balm with sunscreen (SPF 30+)
• Avoid picking or peeling the scab
• Wash hands frequently
• Avoid sharing utensils, towels, or lip products
• Avoid kissing or oral contact during active outbreaks

Picking at a cold sore can delay healing and increase the risk of scarring or infection.

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How Long Is Too Long?

Here's a simple guide:

• 7–14 days → Normal healing time
• More than 2 weeks → Consider medical evaluation
• More than 3 weeks → Definitely see a doctor

If a sore repeatedly appears in the exact same spot and never fully heals, your doctor may consider a biopsy to rule out rare but serious conditions like skin cancer.

This is uncommon, but persistent non-healing sores always deserve medical attention.

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Can Stress Alone Cause a Cold Sore to Linger?

Stress doesn't just trigger outbreaks — it can prolong them. Chronic stress affects immune function, making it harder for your body to suppress viral activity.

Helpful steps include:

• Prioritizing sleep
• Managing stress with relaxation techniques
• Staying hydrated
• Eating balanced meals
• Avoiding excessive alcohol

These won't eliminate HSV-1, but they can reduce recurrence and speed healing.

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The Bottom Line

A cold sore that won't heal is usually not dangerous — but it shouldn't be ignored.

Most cold sores resolve within two weeks. If yours is lasting longer, becoming more painful, spreading, or frequently returning, there may be:

• A secondary infection
• Delayed treatment
• An incorrect diagnosis
• An underlying health issue

Start by monitoring your symptoms carefully. If you want to better understand what might be causing your symptoms, try Ubie's free AI-powered Blistering Symptom Checker for personalized insights before your doctor visit.

Most importantly, speak to a doctor if:

• The sore lasts beyond two weeks
• It involves your eye
• You have a weakened immune system
• You experience severe pain or fever
• Something simply doesn't feel right

Cold sores are common and manageable. But persistent or unusual symptoms deserve professional attention. Early treatment can shorten healing time, reduce complications, and help you feel better faster.