Cold sores are caused by the herpes simplex virus (usually HSV-1). Once you catch the virus, often during childhood from a simple kiss or hug from a relative, it stays in your body for life. Most of the time it sleeps quietly, but every now and then, it can wake up and trigger a cold sore.
What to Expect: The Cold Sore Timeline
If you feel a cold sore coming on, it usually goes through five distinct stages over 10 to 14 days:
The early tingle · Days 1–2
You'll feel a burning, itching, or tingling spot around your lips before anything is visible. Start treatment now for the best results!
Blisters appear · Days 2–3
Small, fluid-filled bumps break out in clusters.
Bursting and oozing · Days 4–5
The blisters pop open, leaving shallow sore spots that leak fluid. This is the most painful stage and when you are most contagious.
Scabbing over · Days 5–8
The sores dry up and form a scab. It may itch, crack, or bleed slightly as you move your mouth.
Final healing · Days 8–14
The scab falls off on its own, leaving fresh, healed skin without leaving a scar.
Is It a Cold Sore or Something Else?
It's easy to confuse cold sores with other common skin or mouth issues:
Cold sore
Happens on the outside of the lips or face; starts with a tingle and forms a hard scab. Highly contagious.
Canker sore (mouth ulcer)
Stays strictly on the inside of your mouth (gums, tongue, inner cheeks). They look like small white or yellow spots with a red border. They are not contagious and not caused by a virus.
Pimple or spot
Red, pus-filled bump that forms around a pore or hair follicle anywhere on the face.
Impetigo
A bacterial infection that creates crusty, honey-colored patches, mostly around a child's nose and mouth.
How Cold Sores Spread & How to Protect Others
Cold sores are contagious from the very first tingle until the scab fully falls off and clean skin is underneath.
How it spreads:
- Direct skin-to-skin contact, like kissing or oral sex.
- Sharing items that touch your mouth, such as lip balm, utensils, cups, or towels.
Protect newborn babies
Never kiss or touch a newborn baby if you have an active cold sore or feel one coming on. The cold sore virus can cause severe, life-threatening illness in infants (known as neonatal herpes).
Common Outbreak Triggers
While you can't get rid of the virus completely, knowing what triggers your outbreaks can help you prevent them. Common triggers include:
- Feeling stressed or run-down
- Being sick with a cold, flu, or fever
- Exposure to bright sunlight or cold winds
- Hormonal changes (like during your period)
- Skin injury or irritation around your mouth
Pro tip: Keep a quick note on your phone when outbreaks happen to spot patterns and figure out your personal triggers.
How to Treat a Cold Sore
While cold sores will usually clear up on their own in 10 to 14 days, starting treatment early can soothe pain and speed up healing.
1. Over-the-counter options
Antiviral creams (like acyclovir / Zovirax)
Applied directly to the spot 4–5 times a day. Best used at the very first tingle to reduce healing time and pain.
Cold sore patches (like Compeed)
Tiny clear hydrocolloid bandages that protect the sore, hide it, absorb fluid, and reduce scabbing.
2. Prescription medications
If you get frequent, severe, or long-lasting outbreaks, a doctor can prescribe oral antiviral tablets (such as acyclovir or valacyclovir).
Single-outbreak pills
Taken at the first sign of symptoms to cut 1 to 4 days off your recovery time.
Daily suppressive therapy
Taken daily if you get frequent outbreaks to prevent the virus from waking up in the first place.
Are There Side Effects?
Cold sore creams and patches rarely cause side effects beyond mild stinging or dryness.
Prescription tablets are generally safe, but can sometimes cause mild temporary side effects, such as:
- Headaches or feeling lightheaded
- Nausea, stomach discomfort, or diarrhea
- Mild skin rash or sun sensitivity
When to seek immediate emergency care
On rare occasions, antiviral pills can cause a severe allergic reaction. Stop taking the medicine and call 911 (or go straight to the nearest emergency department) if you experience:
- • Swelling of your face, lips, tongue, or throat
- • Trouble breathing or severe wheezing
- • Hives or sudden dizziness and collapse
Simple Everyday Prevention Tips
Wash your hands often
Always scrub with soap after touching your face or applying cold sore cream.
Hands off
Avoid touching, picking, or popping the blisters or scabs.
Protect your lips
Use a daily lip balm with SPF 30 or higher when going outside in the sun.
Don't share
Keep your own towels, eating utensils, cups, and lip products during an outbreak.
Rest up
Prioritize good sleep, healthy food, and stay hydrated to keep your immune system strong.
When Should You See a Doctor?
Most cold sores heal fine at home, but check in with a healthcare provider if:
- Your sore hasn't started healing after 10 days.
- The sore is extremely large, painful, or spreads near your eyes.
- You have a weakened immune system (due to illness, chemotherapy, or medications).
- You get cold sores very frequently throughout the year.
- You aren't completely sure if what you have is a cold sore.
This article provides general information about cold sores and is not medical advice. Speak with a healthcare provider about your own symptoms and treatment. For medical emergencies, call 911.