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May 10, 2024

Everyday Health

Fight Cold Sores with Acyclovir

Cold Sores

A "cold sore" refers to a common viral infection caused by the herpes simplex virus (HSV). Cold sores generally appear as blisters around the mouth. The primary way to contract HSV is through direct contact with an active cold sore on another person. Once infected with HSV, the virus remains in the body for life. This lifelong presence doesn't mean that symptoms are constant; rather, the virus can reactivate periodically, leading to new cold sores. Cold sores are most contagious during their active phase, which can sometimes be difficult to identify in the initial stages of reactivation.

Acyclovir Cream

Acyclovir cream is a topical medication used to treat cold sores. It is one of several treatment options for cold sores, which also include oral medications.

Typically, cold sores can resolve on their own within 1-2 weeks without any medical treatment. However, because cold sores can cause discomfort and be cosmetically unappealing, many seek treatment. Acyclovir cream works by inhibiting the replication of the herpes simplex virus, which causes cold sores. By preventing the virus from multiplying, the cream can reduce the duration and severity of an outbreak. Although acyclovir cream is not a cure for herpes simplex virus infections, it effectively manages the symptoms during flare-ups.


Acyclovir cream should be applied as soon as you notice the initial signs of a cold sore, which typically include a tingling, burning, or itching sensation, or the appearance of a red sore near the lips or mouth. To use the cream effectively:

  • Clean Hands: Always wash your hands thoroughly before applying the cream to prevent further infection.
  • Application: Gently apply the cream to the affected area five times per day for four days. Be sure to cover the entire affected area, including the outer edges.
  • Avoid Other Products: Do not apply any other skin products over the treated area and avoid touching or rubbing the cold sore, as this can aggravate the condition.
  • Specific Use: Apply the cream only to the lips and the skin around the mouth. It is not intended for use inside the mouth, eyes, or on genital herpes.

Side Effects

Most of the common side effects of acyclovir cream occur at the site of application. Other side effects include eye symptoms such as:

  • Dry lips
  • Feeling/flaking skin
  • A burning or stinging on application

These are, however, not all the possible side effects of this cream. If you are noticing unpleasant side effects from using acyclovir cream, make sure to speak with a healthcare provider before continuing to use the cream.

Other Forms of Acyclovir

Acyclovir is available in several forms, not just as a topical cream. Each form is used to treat different types of viral infections:

  • Oral Tablets: Acyclovir tablets are commonly prescribed for the treatment of various herpes virus infections beyond just cold sores. These include genital herpes, shingles (herpes zoster), and chickenpox. The tablets work systemically to reduce the severity and duration of these infections by inhibiting viral replication.
  • Eye Drops: For eye-specific viral infections, acyclovir is formulated as eye drops. These are particularly used for treating herpes simplex virus infections that affect the eyes, such as herpetic keratitis. The eye drops target the virus locally in the eye, helping to reduce symptoms and prevent further damage to the eye tissues.
  • Intravenous Solutions: In more severe cases, particularly in hospitalized patients, acyclovir can be administered intravenously. This is often used for severe infections such as encephalitis (inflammation of the brain) caused by herpes viruses, or severe cases of shingles or chickenpox in immunocompromised patients.


  1. Herpes Simplex Virus (HSV) Mouth Infection. Cedars Sinai. (n.d.). Retrieved December 18, 2023, from
  2. ZOVIRAX® (acyclovir) cream 5% for topical use. Food and Drug Administration. (2002, Revised 04/2014). Retrieved December 18, 2023, from

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