Anbesol Cold Sore Therapy Side Effects: What to Expect and When to Call Your Doctor

Anbesol Cold Sore Therapy is widely used and generally considered safe for most adults and children over 2 years old when used as directed. However, like all products containing benzocaine, it carries one serious potential side effect — methemoglobinemia — as well as a range of milder effects. Here's a complete breakdown of what to expect, what to watch for, and when to seek emergency care.

Common Side Effects (Expected and Mild)

Most people using Anbesol Cold Sore Therapy experience no side effects beyond the following expected and typically mild responses:

• Temporary stinging or burning at the application site. This occurs briefly when benzocaine is first applied and resolves as the numbing effect takes over — usually within 30–60 seconds. This is normal and not a sign of an adverse reaction.
• Temporary numbness. This is the intended effect of benzocaine — numbing the nerve endings at the cold sore site. It typically lasts 15–30 minutes per application.
• Mild skin irritation or redness. Some people experience minor local irritation at the application site. This is usually self-limiting. If redness worsens or spreads significantly, discontinue use.
• Camphor cooling sensation. The 3% camphor in the formula creates a mild cooling and tingling sensation that most users find soothing.

Serious Warning: Methemoglobinemia from Benzocaine

The most important safety warning on Anbesol Cold Sore Therapy's label is the methemoglobinemia warning. This warning is required by the FDA on all benzocaine-containing products.

Methemoglobinemia is a condition in which benzocaine oxidizes hemoglobin to methemoglobin — a form that cannot carry oxygen effectively. This reduces the amount of oxygen delivered to the body's tissues. The condition is rare from topical application to a small area like a cold sore, but it can be serious and potentially life-threatening if it occurs.

Critically: this can occur even on your first use, or after many prior uses without incident.

Stop use and seek immediate emergency medical attention if you or anyone in your care develops any of these signs after using Anbesol Cold Sore Therapy:

• Pale, gray, or blue-colored skin (cyanosis), especially around the lips, fingernails, or eyes
• Headache, especially if sudden or severe
• Rapid or irregular heart rate
• Shortness of breath or difficulty breathing
• Dizziness or lightheadedness
• Fatigue or unusual lack of energy

Allergic Reactions: What to Watch For

Some individuals are allergic to benzocaine or other "caine" anesthetics (procaine, butacaine, tetracaine). If you have a known allergy to any of these, do not use Anbesol Cold Sore Therapy. Signs of an allergic reaction include:

• Hives or rash (especially spreading beyond the application site)
• Swelling of the face, lips, tongue, or throat (angioedema)
• Difficulty breathing or wheezing

These signs indicate anaphylaxis — a medical emergency. Call 911 immediately.

Who Should NOT Use Anbesol Cold Sore Therapy

Do not use Anbesol Cold Sore Therapy if you:

• Are allergic to benzocaine, procaine, butacaine, or any "caine" local anesthetic
• Are applying to a child under 2 years of age (FDA-contraindicated)
• Have G6PD deficiency (significantly increases methemoglobinemia risk)
• Are applying to deep wounds, puncture wounds, infections, or lacerations (OTC label contraindication)

Stop Use and Ask a Doctor If:

Per the product label, you should stop use and consult a doctor if:

• Your condition worsens during use
• Symptoms persist for more than 7 days
• Symptoms clear up and then recur within a few days

Safe Use Tips

To minimize risk and maximize benefit from Anbesol Cold Sore Therapy:

1. Apply only to the affected cold sore area — not over large areas of skin
2. Do not exceed 3–4 applications per day
3. Avoid contact with eyes and mucous membranes
4. Store at room temperature (68–77°F); do not refrigerate
5. Do not use on children under 2 years of age under any circumstances

The Bottom Line on Side Effects

For most adults who apply Anbesol Cold Sore Therapy correctly to a small cold sore area, side effects are minor — a brief sting that resolves quickly. The serious methemoglobinemia warning is important to know about but is rare in practice when the product is used as directed. Be aware of the warning signs and respond quickly if they occur. For information on potential drug interactions, see our guide to Anbesol Cold Sore Therapy drug interactions. If you need help finding this product in stock, medfinder can locate it at pharmacies near you.