A cold sore or fever blister is caused by the herpes simplex virus (HSV). About 2 of every 3 adults under age 50 carries HSV type 1 (HSV-1), which is why this virus is the most common cause of cold sores — although HSV type 2 is also a possible culprit. (1)
Once a person is infected, the virus enters the body and travels to the nerves, where it lies dormant until awakened. (2)
Those infected by HSVcan develop multiple cold sores throughout their life, yet some people exposed to the virus never get a cold sore. (3)
Cold sores are sometimes mistaken for other lesions that form in or around the mouth, such as canker sores. Since cold sores are contagious, it’s important that you know how to distinguish these sores from other sores and take the appropriate steps to stop the spread of the virus. (1)
‘Do I Have a Cold Sore?’ Telltale Signs and Symptoms
The symptoms of a cold sore vary depending on whether it’s your first outbreak or a recurrent outbreak. (1)
A cold sore causes tiny clusters of fluid-filled blisters on or around the lip or mouth. Unlike canker sores, cold sores don’t usually develop inside the mouth. But a first-time infection with HSV can produce a condition called acute herpetic gingivostomatitis, which is a painful eruption that causes swollen red gums, a fever, enlarged lymph nodes, and numerous sores on the tongue, lips, and inner cheeks, says Allison Arthur, MD, a board-certified dermatologist at Sand Lake Dermatology Center in Orlando, Florida. (4)
Many people who have cold sores were exposed to HSV-1 during childhood, most likely after being kissed by someone who had the virus. Cold sore symptoms tend to be worse during the primary or first outbreak, with some people experiencing milder symptoms with recurrent outbreaks. (2)
Other symptoms may occur if you’re newly infected, too: (4)
- Sore throat
- Body aches
- Pain with swallowing
Cold sores start with an itchy or tingling sensation in the spot of development. This can last for one or two days, with a cold sore developing shortly thereafter. Other symptoms include redness, pain, or swelling at the spot of the sore. (1)
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After a few days, cold sores rupture and ooze pus. A scab forms over the sore in its final stages. Cold sores heal in about one to two weeks without treatment, but they can heal sooner with treatment. (4)
While cold sores often occur on or around the lips, they can also develop around the nose, cheek, and genital area. (1) This can happen if you touch a cold sore and then touch another part of your body without washing your hands or if you engage in oral sex with someone who has a cold sore.
The virus can also spread to your eyes and cause a serious eye infection. So it’s important that you don’t touch your eyes if you have a cold sore.
Signs that the virus has spread to your eyes include sensitivity to light, swelling, or irritation around your eye. (3)
What to Know About How Cold Sores Are Diagnosed
See a doctor if you’re not sure whether a lesion is a cold sore. In most cases, your doctor can diagnose a cold sore by looking at the lesion. To confirm a diagnosis, however, your doctor may take a fluid sample from the blister and send it to a lab to check for HSV-1. (4)
Keep in mind that you don’t have to see a doctor for a cold sore. These are common infections that will clear on their own. Nonetheless, many medications can relieve symptoms and speed the healing process. These include over-the-counter antiviral medications, as well as oral pain relief creams and ointments.
Cold sores typically heal in about 7 to 10 days, so see a doctor if your sore doesn’t improve after two weeks, advises Amesh Adalja, MD, a senior scholar at Johns Hopkins Center for Health Security who is based in Pittsburgh. (5)
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In this situation, you may need a prescription antiviral medication, especially if you have an autoimmune disease or a weak immune system. Both factors will make it harder for your body to fight the virus. (5)
Also, see a doctor if you have recurrent cold sores. Your doctor may prescribe an antiviral medication for everyday use, which can reduce the frequency and duration of outbreaks. An antiviral can also prevent the virus from spreading to your spinal cord or brain. (1)
An antiviral is sometimes prescribed to people who have eczema. “In people with an underlying widespread skin disease, such as eczema, a cold sore outbreak can spread like wildfire throughout the skin, causing a severe infection known as eczema herpeticum,” says Dr. Arthur. (5)
You should also seek medical attention if a cold sore spreads to your eyes. This type of eye infection can lead to complications such as scarring or vision problems. (4)
A Final Word on Cold Sores Symptoms and Their Diagnosis
There’s no cure for HSV-1, so cold sores may return after treatment. (1) But recognizing the signs and symptoms of a cold sore and starting treatment early may shorten the duration of an outbreak. And for those who live with frequent outbreaks, a daily antiviral might reduce the frequency of cold sores.