How Long Is a Cold Sore Contagious?

  • Medical Reviewer: Dany Paul Baby, MD
Medically Reviewed on 7/8/2022

What are cold sores?

Cold sores are blisters around your mouth and lips. Cold sores are contagious until they are completely healed.
Cold sores are blisters around your mouth and lips. Cold sores are contagious until they are completely healed.

If you begin to develop small blisters around your mouth and lips, you may have cold sores. Until your cold sores are completely healed, they are contagious, so you should take precautions to avoid passing your cold sores on to others. 

Sometimes called fever blisters, oral herpes, or herpes labialis, cold sores are a typical viral infection. They appear in the form of small blisters filled with fluid on and near your mouth. They usually come in groups and can take a few weeks to heal. After a blister appears, it will break, form a scab, and then fade away.

If you come into close contact with someone, like kissing them, while you have an active cold sore, the infection may spread. There is no cure for cold sores – they will sporadically reappear as part of a chronic condition. There are treatment options that will help you handle outbreaks and minimize symptoms, though.

Symptoms of cold sores

Your cold sores will likely go through a few stages before disappearing:

  • Stage one includes tingling and itching. The area around your lips may burn, itch, or tingle for a day or two.
  • Stage two comes immediately after stage one. Little, hard spots will show up and become painful, fluid-filled blisters. This usually happens near the border of your lips, around your nose, inside your mouth, or on your cheeks.
  • Stage three consists of oozing and crusting. Small blisters grouped together may merge and pop. This leaves shallow, open sores that become gummy and then crusty.
  • Stage four is the final stage. The crusty scab will fall off naturally, usually leaving new-looking skin behind.

Depending on whether or not you’ve had fever blisters before, this cycle may look different. Your first cold sore might not show up until a few weeks after you were exposed to the infection. Then, the fluid-filled sores can last up to a week before the scabs form. You might be in stage three for three weeks before your cold sores are totally healed. 

The initial outbreak is often the most severe, and the flare-ups that follow will likely be less extreme.

During your first outbreak, you might also have:

If you do get the cold sore virus, it’s not guaranteed that you’ll show symptoms. Plenty of adults have the virus, but it is never activated, and therefore, they never develop cold sores.

Cold sore causes

Cold sores are also known as oral herpes because the herpes simplex virus type 1 causes these chronic blisters. This infection is extremely common and contagious; it spreads through close contact or saliva. 

Methods of spreading include:

  • Kissing
  • Sharing utensils
  • Sharing straws
  • Sharing towels
  • Sharing lip balm
  • Any similar action

You can share or contract the virus from exposure to blisters in any stage. As long as the cold sores are not fully healed, they are contagious.

After you are initially infected with herpes simplex virus type 1, you’ll continue experiencing cold sore flare-ups. The infection will stay dormant in the cells around your mouth until something triggers them. 

Triggers are unique to each person but could include:

  • Exposure to the sun
  • Pregnancy, menstruation, or other hormonal changes
  • Extreme heat or cold
  • Physical or emotional stress
  • Exhaustion
  • Fever or illness, like the flu or a cold
  • Dry, cracked, or otherwise damaged lips

Treating a cold sore

There are plenty of things you can do at home to help your cold sores heal:

  • Eating soft, cool food
  • Washing your hands before and after applying creams or ointments to your cold sores
  • Avoiding the things that trigger your cold sores
  • Using sunblock lip balm when you go outside
  • Taking ibuprofen or paracetamol for any pain or swelling
  • Staying hydrated
  • Using over-the-counter antiviral creams/ointments or cold sore patches
  • Applying a cool compress for a few minutes at a time using a clean towel

Alternatively, you should avoid certain things to not irritate or spread your cold sores:

  • Kissing
  • Having oral sex
  • Touching your cold sores without washing your hands first
  • Rubbing cream or ointment on your cold sores (dab instead)
  • Eating foods high in salt or acid

Your cold sores will likely heal on their own, but you might need to visit your healthcare provider if they’re abnormally large, painful, or frequently occurring. They may be able to prescribe antiviral tablets to keep cold sore flare-ups at bay.

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Who can get a cold sore?

Nearly anybody can get cold sores. However, you’re most likely to experience complications if you have had one of the following conditions or treatments and have a weakened immune system as a result:

Complications of cold sores

Although herpes simplex virus type 1 primarily affects the mouth area, it’s possible to experience complications in other parts of the body.

  • Eyes. This virus can result in an eye infection. If you continue getting eye infections, your eyes can scar and experience loss of vision.
  • Fingertips. Herpes simplex virus type 1 can spread to the ends of your fingers, also known as herpes whitlow. This is common in children with cold sores who habitually suck their thumbs.
  • Large areas of skin. If you have eczema, you’re at a higher risk of spreading cold sores across any part of your body. This is an extremely serious case of herpes simplex virus type 1 and should be addressed immediately.
  • Genitals. Oral sex can cause ulcers or warts on your anus or genitals. Don’t confuse herpes simplex virus type 1 with the common STI known as herpes, though. Cold sores are not associated with a sexually transmitted infection.

Serious complications can follow if newborns develop cold sores. If your baby is under six months old and gets cold sores, they may experience high fevers and seizures. Their underdeveloped immune systems aren’t prepared to handle this virus.

When to see a doctor for a cold sore

Although cold sores usually go away without serious medical intervention, you should get in touch with your healthcare provider immediately if:

  • Your immune system is weak
  • Your cold sores haven’t healed after two weeks
  • Your symptoms are extreme
  • You frequently experience flare-ups
  • Your eyes become irritated

Be patient as you endure cold sore flare-ups. At the same time, you know your condition and symptoms best! If you feel that you need medical attention, seek it.

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Medically Reviewed on 7/8/2022
References
Sources:

Cleveland Clinic: "Cold Sores."

Mayo Clinic: "Cold sore."

National Health Service: "Cold Sores."