Cold Sores: Symptoms, Causes & Treatment Guide

Cold sores, also known as fever blisters or oral herpes, are small, painful blisters that typically appear on or around the lips. They are caused by the herpes simplex virus type 1 (HSV-1), which infects approximately 67% of the global population under age 50. While cold sores cannot be cured, they usually heal within 7-10 days and can be effectively managed with antiviral medications and home care.

What Are Cold Sores and What Causes Them?

Cold sores are small, fluid-filled blisters caused by the herpes simplex virus type 1 (HSV-1). The virus spreads through direct contact with infected saliva or blister fluid, enters the body through breaks in the skin, and then lies dormant in nerve cells until triggered to reactivate. Once infected, the virus remains in your body for life, though many people never experience symptoms.

Cold sores, medically known as herpes labialis, are one of the most common viral infections worldwide. The World Health Organization estimates that approximately 3.7 billion people under age 50—about 67% of the global population—have HSV-1 infection. While the virus is most often acquired during childhood through non-sexual contact such as a kiss from a family member, it can also be transmitted later in life.

The herpes simplex virus belongs to the Herpesviridae family and exists in two main types: HSV-1 and HSV-2. Historically, HSV-1 was associated primarily with oral infections (cold sores), while HSV-2 was linked to genital herpes. However, this distinction has become less clear in modern times, as HSV-1 is now responsible for an increasing number of genital herpes cases, typically transmitted through oral-genital contact.

After the initial infection, the virus travels along nerve fibers to the trigeminal ganglion—a cluster of nerve cells near the ear—where it establishes a lifelong latent (dormant) infection. The virus can reactivate at any time, traveling back along the nerve to the skin surface where it causes a new outbreak. This explains why cold sores typically recur in the same location on the lip or face.

How HSV-1 Differs from HSV-2

While both types of herpes simplex virus can cause oral and genital infections, there are important differences between them. HSV-1 is more commonly associated with oral infections and tends to cause less severe recurrences when it affects the genital area. HSV-2, on the other hand, is more typically associated with genital infections and tends to reactivate more frequently than HSV-1.

Understanding which type of virus you have can be important for predicting the frequency and severity of future outbreaks, as well as for counseling about transmission risks. Blood tests can distinguish between HSV-1 and HSV-2 antibodies, though these tests cannot determine where in the body the infection is located.

What Are the Symptoms of a Cold Sore?

Cold sore symptoms typically progress through five stages over 7-10 days: tingling/itching (prodrome), blistering, weeping/ulceration, crusting, and healing. The first sign is usually a tingling, burning, or itching sensation on the lip 1-2 days before blisters appear. Recognizing this early warning sign is crucial, as starting treatment during the prodrome stage significantly improves outcomes.

The presentation of cold sores can vary significantly between individuals and between first-time infections and recurrences. Understanding the typical progression of symptoms can help you recognize an outbreak early and start treatment promptly, which is key to reducing severity and duration.

The Five Stages of a Cold Sore Outbreak

Cold sores typically progress through a predictable sequence of stages, though the duration and intensity of each stage can vary between individuals. Knowing these stages helps you understand what to expect and when treatment is most effective.

• Stage 1 - Prodrome (Days 1-2): Tingling, itching, or burning sensation at the site where the cold sore will appear. This is the optimal time to start antiviral treatment.
• Stage 2 - Blistering (Days 2-4): Small, fluid-filled blisters form, often in clusters. The area becomes red, swollen, and painful.
• Stage 3 - Weeping/Ulceration (Days 4-5): Blisters burst and merge, forming a shallow, painful ulcer. This is the most contagious stage.
• Stage 4 - Crusting (Days 5-8): A yellowish-brown crust forms over the ulcer. Cracking of the crust may cause bleeding and discomfort.
• Stage 5 - Healing (Days 8-10): The scab falls off, revealing new pink skin underneath. Complete healing occurs without scarring in most cases.

First Outbreak vs. Recurrent Outbreaks

The primary (first) infection with HSV-1 is often the most severe, particularly when it occurs in childhood. Many children experience their first HSV-1 infection as gingivostomatitis—a condition characterized by widespread painful sores throughout the mouth, swollen and bleeding gums, high fever, difficulty eating and drinking, and swollen lymph nodes in the neck. This primary infection can last 2-3 weeks and may be mistaken for other conditions like strep throat or hand-foot-and-mouth disease.

In contrast, recurrent outbreaks are typically much milder. About one-third of people who have been infected with HSV-1 experience recurrent cold sores. These recurrences are usually limited to a small cluster of blisters on or near the lip, cause less systemic symptoms (no fever or swollen glands), and heal more quickly—typically within 7-10 days. Many people also notice that their outbreaks become less frequent and less severe as they age.

How Do Cold Sores Spread to Others?

Cold sores spread primarily through direct contact with infected saliva or blister fluid during kissing, sharing utensils, or oral-genital contact. The virus is most contagious when visible blisters are present, but can also spread during the "prodrome" phase (before blisters appear) and through "asymptomatic shedding" when no symptoms are visible. The incubation period from exposure to first symptoms is typically 2-12 days.

Understanding how HSV-1 spreads is essential for protecting yourself and others. The virus requires direct contact with infected secretions—it cannot survive long on surfaces or spread through the air. However, the virus can be shed (released from the body) even when no visible symptoms are present, which is why transmission can occur unexpectedly.

The most common routes of transmission include direct contact with an active cold sore or the fluid inside blisters, kissing someone who has an active outbreak or is shedding virus asymptomatically, sharing items that touch the mouth such as utensils, drinking glasses, towels, lip balm, or razors, and oral-genital contact, which can transmit HSV-1 from mouth to genitals (or vice versa).

Periods of Highest Contagiousness

The risk of transmitting HSV-1 is not constant—it fluctuates depending on the stage of infection. Understanding these periods of heightened contagiousness can help you take appropriate precautions.

The weeping/ulceration stage (when blisters have burst and are oozing) represents the period of highest viral shedding. During this time, the concentration of virus particles in the fluid is extremely high, making transmission very likely with any direct contact. The prodrome stage (tingling sensation before blisters appear) is also a high-risk period, as the virus is actively replicating just below the skin surface.

Once a scab has formed and dried, the risk of transmission decreases significantly. However, picking at or disturbing the scab can release virus particles and increase transmission risk. Even after visible symptoms have resolved, asymptomatic viral shedding can occur—studies suggest this happens on approximately 5-10% of days in people with HSV-1 infection, though individual rates vary considerably.

What Triggers Cold Sore Outbreaks?

Common cold sore triggers include physical or emotional stress, sun exposure (UV light), fever or illness, fatigue and lack of sleep, hormonal changes (such as menstruation), weakened immune system, and physical trauma to the lips. Identifying and avoiding your personal triggers can help reduce the frequency of outbreaks.

After the primary infection, HSV-1 establishes itself in nerve cells where it remains dormant until something triggers it to reactivate. While the exact mechanisms that trigger reactivation are not fully understood, researchers have identified several common factors that appear to precipitate outbreaks in susceptible individuals.

Stress—whether physical or emotional—is one of the most commonly reported triggers. Stress hormones like cortisol can suppress immune function, potentially allowing the dormant virus to reactivate. Studies have shown correlations between periods of high stress (exams, work deadlines, emotional crises) and increased frequency of cold sore outbreaks.

Sun exposure is another well-documented trigger, particularly exposure to ultraviolet (UV) light. The mechanism involves UV-induced damage to the skin and local immune suppression, which can trigger viral reactivation. This is why many people notice cold sores appearing after a day at the beach or skiing without adequate lip protection. Using lip balm with SPF 30 or higher can help prevent sun-triggered outbreaks.

Additional Common Triggers

Illness and fever are closely associated with cold sore outbreaks—hence the alternative name "fever blisters." During illness, the immune system is occupied fighting another infection, potentially allowing HSV-1 to reactivate. Additionally, fever itself may directly contribute to reactivation.

Hormonal changes appear to trigger outbreaks in some people, particularly women who notice cold sores appearing around the time of menstruation. The fluctuations in estrogen and progesterone levels during the menstrual cycle may affect immune function and susceptibility to viral reactivation.

Other reported triggers include fatigue and lack of sleep, physical trauma to the lips (dental work, cosmetic procedures, vigorous kissing), cold weather and dry conditions, and certain foods (though scientific evidence for dietary triggers is limited).

What Can You Do at Home for Cold Sores?

Home care for cold sores focuses on relieving symptoms and promoting healing. Apply over-the-counter antiviral cream (docosanol/Abreva) at the first sign of tingling, keep the area clean and dry, avoid picking at blisters or scabs, apply ice wrapped in cloth for pain relief, use lip balm to prevent cracking, and take over-the-counter pain relievers as needed. Do not apply regular cosmetics, makeup, or moisturizers to active cold sores.

While cold sores will heal on their own, proper self-care can reduce discomfort, speed healing, and prevent complications like secondary bacterial infection. Starting treatment at the first sign of a cold sore—during the tingling "prodrome" stage—provides the best results.

Over-the-Counter Treatments

Docosanol (Abreva) is the only FDA-approved over-the-counter antiviral cream for cold sores. It works by preventing the virus from entering healthy cells and spreading. For best results, apply it five times daily at the first sign of a cold sore and continue until the lesion has healed. Studies show that docosanol can reduce healing time by about half a day to a day when used early.

Cold sore patches (hydrocolloid bandages specifically designed for cold sores) are another option. These patches create a protective barrier over the sore, which can reduce pain, hide the blemish, and potentially reduce transmission risk. Some patches contain ingredients like tea tree oil that may have mild antiviral properties.

For pain relief, over-the-counter analgesics like ibuprofen or acetaminophen can help with discomfort. Applying ice wrapped in a cloth to the area can reduce swelling and provide temporary numbing. Some people find relief from topical anesthetic products containing benzocaine or lidocaine, though these should be used sparingly as they can cause skin irritation.

What to Avoid During an Outbreak

Do not pick at, squeeze, or pop cold sore blisters. This can spread the virus to other areas of your face, introduce bacteria causing secondary infection, delay healing, and increase scarring risk. Similarly, avoid removing the scab prematurely—let it fall off naturally when the skin underneath has healed.

Avoid applying regular lip products, makeup, or moisturizers to active cold sores. These products are not formulated for broken skin and may contain ingredients that irritate the sore or interfere with healing. Additionally, the virus can contaminate the product, potentially spreading infection.

When Should You See a Doctor for Cold Sores?

See a doctor if: this is your first cold sore outbreak (especially with severe symptoms), cold sores haven't healed after 2-3 weeks, you have frequent outbreaks (more than 6 per year), you have a weakened immune system, you develop eye pain or vision changes, you're pregnant and get cold sores for the first time, or an infant develops signs of herpes infection. Seek emergency care for difficulty breathing, high fever with widespread blisters, or suspected herpes in a newborn.

Most cold sores can be managed at home and heal without complications. However, certain situations warrant professional medical evaluation and treatment. Knowing when to seek care can prevent complications and ensure you receive appropriate treatment.

Situations Requiring Medical Attention

First-time outbreaks, particularly severe ones, should be evaluated by a healthcare provider. Primary HSV-1 infection can sometimes be severe, especially in children (gingivostomatitis) or immunocompromised individuals. A doctor can confirm the diagnosis, prescribe antiviral medication to reduce severity and duration, and provide guidance on managing symptoms.

Eye involvement requires prompt medical attention. If you experience eye pain, redness, tearing, light sensitivity, or vision changes during a cold sore outbreak, see a doctor immediately. Herpes keratitis (HSV infection of the cornea) can cause scarring and vision loss if not treated promptly with antiviral eye drops or ointment.

Frequent recurrences—generally defined as six or more outbreaks per year—may benefit from suppressive antiviral therapy. This involves taking a daily antiviral medication to prevent outbreaks from occurring. Studies show that suppressive therapy can reduce outbreak frequency by 70-80%.

How Are Cold Sores Treated with Medication?

Prescription antiviral medications are the most effective treatment for cold sores. Acyclovir, valacyclovir, and famciclovir can be taken orally to reduce outbreak duration and severity. These medications work best when started within 24-48 hours of symptom onset. For frequent recurrences, daily suppressive therapy can prevent outbreaks. Topical prescription antivirals (acyclovir cream, penciclovir cream) are also available but are less effective than oral medications.

While cold sores will eventually heal without treatment, antiviral medications can significantly reduce the duration and severity of outbreaks, especially when started early. These medications work by inhibiting viral replication—they cannot eliminate the virus from your body, but they can control active infections and prevent recurrences.

Oral Antiviral Medications

Acyclovir (Zovirax) was the first antiviral developed for herpes infections and remains widely used. It can be taken as a 400mg tablet five times daily for 5 days to treat an outbreak, or at a lower dose of 400mg twice daily for suppressive therapy. Acyclovir is generally well-tolerated, with headache and nausea being the most common side effects.

Valacyclovir (Valtrex) is a prodrug of acyclovir that offers improved absorption, allowing for less frequent dosing. For cold sore treatment, a two-day regimen of 2000mg twice daily (on day 1) followed by 1000mg twice daily (on day 2) is often prescribed. For suppression, 500mg-1000mg once daily is typical. Valacyclovir is particularly convenient for episodic treatment.

Famciclovir (Famvir) is another oral antiviral option. It can be taken as a single 1500mg dose at the first sign of a cold sore, making it very convenient for episodic treatment. This medication is especially useful for people who want the simplest possible regimen.

Topical Prescription Treatments

Acyclovir 5% cream (Zovirax cream) and penciclovir 1% cream (Denavir) are prescription topical antivirals. They must be applied frequently (every 2-4 hours while awake) for several days. While convenient, topical treatments are generally less effective than oral medications, as they cannot reach the virus at its source in the nerve cells. They may be appropriate for people who prefer not to take oral medication or as an adjunct to systemic treatment.

How Can You Prevent Cold Sore Outbreaks?

Prevent cold sore outbreaks by avoiding known triggers, using SPF 30+ lip balm when exposed to sun, managing stress, getting adequate sleep, and maintaining overall health. Prevent spreading to others by avoiding kissing and intimate contact during outbreaks, not sharing personal items, washing hands frequently, and using barrier protection during oral sex. If you have frequent outbreaks, ask your doctor about daily suppressive antiviral therapy.

While there is no way to completely eliminate the risk of cold sore recurrences once you're infected with HSV-1, several strategies can help reduce outbreak frequency and prevent transmission to others. Prevention focuses on two areas: avoiding triggers that reactivate the virus and preventing spread to uninfected individuals.

Reducing Outbreak Frequency

Sun protection is one of the most effective preventive measures. UV exposure is a well-documented trigger for cold sore outbreaks. Always use a lip balm with SPF 30 or higher when spending time outdoors, and reapply every 2 hours or after swimming or sweating. Wide-brimmed hats and seeking shade during peak sun hours provide additional protection.

Stress management can help reduce outbreak frequency, as stress is a major trigger for many people. Techniques such as regular exercise, adequate sleep, mindfulness meditation, and maintaining social connections can help manage stress levels. If you notice that stressful periods consistently trigger outbreaks, consider having antiviral medication on hand to start treatment at the first sign of symptoms.

Suppressive therapy with daily antiviral medication is highly effective for people with frequent outbreaks. Studies show that daily valacyclovir or acyclovir can reduce outbreak frequency by 70-80%. This approach may be recommended for people with six or more outbreaks per year, those who find outbreaks particularly distressing, or individuals who want to reduce the risk of transmitting HSV-1 to partners.

Preventing Transmission

To prevent spreading cold sores to others, avoid kissing and intimate contact when you have visible sores or feel one coming on, don't share utensils, cups, towels, or lip products, wash hands frequently, especially after touching the affected area, consider using barrier protection during oral sex, and inform partners about your HSV-1 status so they can make informed decisions.

What Are the Possible Complications of Cold Sores?

Most cold sores heal without complications, but potential complications include secondary bacterial infection (requiring antibiotics), herpes keratitis (eye infection that can affect vision), eczema herpeticum (severe spread in people with eczema), and rarely, herpes encephalitis (brain infection). Newborns and immunocompromised individuals are at highest risk for serious complications.

For the vast majority of people with healthy immune systems, cold sores are a nuisance rather than a serious health threat. However, certain populations are at increased risk for complications, and everyone should be aware of warning signs that require medical attention.

Secondary Bacterial Infection

The open sores created by cold sores can become infected with bacteria, particularly Staphylococcus or Streptococcus species. Signs of secondary bacterial infection include increased redness spreading beyond the original sore, increased swelling and warmth, pus or yellow discharge, increasing pain, and fever. If you suspect a bacterial infection, see a doctor—you may need antibiotic treatment in addition to antiviral medication.

Herpes Keratitis (Eye Infection)

HSV can infect the cornea of the eye, causing herpes keratitis. This can occur if you touch a cold sore and then rub your eyes, transferring the virus. Symptoms include eye pain, redness, excessive tearing, light sensitivity, blurred vision, and the sensation of something in the eye. Herpes keratitis requires prompt treatment with antiviral eye drops or ointment to prevent corneal scarring and vision loss. Always wash hands thoroughly after touching a cold sore.

Eczema Herpeticum

People with atopic dermatitis (eczema) are at risk for eczema herpeticum—a severe, widespread HSV infection that spreads across areas of damaged skin. This appears as numerous painful blisters in eczematous areas, often accompanied by fever and malaise. Eczema herpeticum requires immediate medical treatment with systemic antiviral medication and sometimes hospitalization.

Neonatal Herpes

HSV infection in newborn babies (neonatal herpes) is rare but extremely serious. Babies can acquire HSV during delivery if the mother has an active genital herpes outbreak, or after birth through contact with someone who has an active cold sore. Symptoms in newborns include lethargy, poor feeding, fever or temperature instability, seizures, and skin blisters. Neonatal herpes is a medical emergency requiring immediate treatment with intravenous antiviral medication.

What Should Pregnant Women Know About Cold Sores?

If you're pregnant and have a history of cold sores, the risk to your baby is very low because antibodies protect the fetus. However, if you get your first HSV-1 infection during pregnancy, consult your healthcare provider immediately, as first-time infections pose greater risk. After delivery, avoid kissing your newborn if you have an active cold sore, and wash hands frequently to prevent transmission.

Cold sores during pregnancy are common and usually not a cause for concern, especially if you've had cold sores before becoming pregnant. However, certain situations require medical attention and careful management.

Recurrent Cold Sores During Pregnancy

If you had HSV-1 before pregnancy and experience recurrent cold sores during pregnancy, your body has already developed antibodies to the virus. These antibodies cross the placenta and provide protection to your developing baby. The risk of transmission to the fetus or newborn from recurrent oral herpes is extremely low. Antiviral medications like acyclovir and valacyclovir are considered safe during pregnancy when indicated, though your doctor will weigh the benefits and risks.

First-Time Infection During Pregnancy

A primary (first-time) HSV infection during pregnancy is more concerning, particularly if it occurs close to the time of delivery. Without existing antibodies, there's a higher risk of transmitting the virus to the baby. If you develop what appears to be your first cold sore outbreak during pregnancy, contact your healthcare provider. They may perform tests to confirm whether it's a new infection and may prescribe antiviral treatment to reduce viral shedding and severity.

Protecting Your Newborn

After delivery, anyone with an active cold sore should take precautions to protect the newborn. Do not kiss the baby when you have a cold sore or feel one coming on, wash hands thoroughly and frequently, especially before handling the baby or preparing bottles, consider wearing a mask to cover the cold sore when holding or feeding the baby, and ensure others who have cold sores follow these same precautions.

What Else Could Look Like a Cold Sore?

Conditions that can be confused with cold sores include canker sores (aphthous ulcers) which occur inside the mouth, angular cheilitis (cracking at mouth corners), impetigo (bacterial skin infection), hand-foot-and-mouth disease (in children), and contact dermatitis. Key differences: cold sores typically appear on or around the lips, are preceded by tingling, form blisters, and are contagious—while canker sores are inside the mouth, not contagious, and don't form blisters.

Several conditions can produce sores in or around the mouth that may be confused with cold sores. Distinguishing between these conditions is important because they have different causes and treatments.

Cold Sores vs. Canker Sores

Canker sores (aphthous ulcers) are the condition most commonly confused with cold sores, but they are distinctly different. Canker sores occur inside the mouth—on the inner lips, cheeks, tongue, or gums—while cold sores typically appear outside the mouth on the lips or surrounding skin. Canker sores are shallow, round ulcers with a white or gray center and red border; they don't form blisters first. Importantly, canker sores are not contagious and are not caused by herpes virus. Their cause is unknown, though triggers may include minor mouth injuries, stress, acidic foods, and vitamin deficiencies.

Angular Cheilitis

Angular cheilitis (also called perleche) is inflammation and cracking at the corners of the mouth. It can be caused by fungal infection (Candida), bacterial infection, or simply dry, irritated skin. Unlike cold sores, angular cheilitis occurs specifically at the mouth corners, doesn't form typical blisters, and may be associated with drooling, denture problems, or nutritional deficiencies. Treatment depends on the underlying cause and may include antifungal or antibiotic creams.

Impetigo

Impetigo is a bacterial skin infection that can produce honey-colored crusted sores around the mouth and nose. It's most common in children and is highly contagious. Unlike cold sores, impetigo is caused by bacteria (usually Staphylococcus aureus or Streptococcus pyogenes) and is treated with antibiotics. The sores of impetigo tend to spread more rapidly and may have a distinct honey-colored crust appearance.