Acyclovir Topical: Cold Sore Uses, How to Apply, Side Effects
Last updated September 7, 2026.
**Acyclovir topical is a prescription antiviral cream or ointment applied directly to the skin or lips to treat herpes simplex virus infections.** Acyclovir gets taken up by virus-infected cells and blocks the enzyme the herpes virus uses to copy its own DNA, which slows the outbreak and shortens healing time. It works best when you start it at the very first sign of an outbreak, ideally during the tingling or burning stage before blisters appear. The most important safety point is that topical acyclovir treats the skin lesion only and does not cure herpes or stop the virus from coming back, so frequent or severe outbreaks usually need oral antiviral treatment instead.
What does it treat?
Acyclovir cream 5 percent is approved for recurrent herpes labialis, the cold sores that show up on the lips and around the mouth, in people age 12 and older. Acyclovir ointment 5 percent is approved for initial episodes of genital herpes and for limited, non-life-threatening herpes simplex skin infections in people with weakened immune systems, such as those on chemotherapy or transplant medicines. The typical pattern it targets is a small cluster of painful blisters on a red base, often preceded by a day of tingling, itching, or burning in the same spot, that crusts over and heals in about a week. A combination product, acyclovir and hydrocortisone cream 5 percent and 1 percent, is also available for cold sores in people age 6 and older and adds a mild steroid to reduce the surrounding inflammation. Topical acyclovir is not used for shingles, chickenpox, or eye infections, which need oral or ophthalmic treatment.
How do you take it?
Acyclovir topical comes as a 5 percent cream and a 5 percent ointment. For cold sores, the label directs you to apply the cream 5 times a day for 4 days, starting as early as possible after the first symptom, and to rub it in until it disappears. For the ointment, the label directs application every 3 hours, 6 times a day, for 7 days, using enough to cover all lesions, which is about a half inch ribbon per 4 square inches of skin. Wear a finger cot or glove when applying the ointment so you do not spread virus to other parts of your body or to other people. There is no daily milligram ceiling the way there is with pills, but do not exceed the number of daily applications on your label or extend the course beyond 4 days for cream or 7 days for ointment without talking to a clinician. Food and alcohol do not affect it, and you can apply it any time of day. Keep it off the inside of your mouth, your eyes, and the vagina, since these products are made for external skin and lip use only. If you miss an application, apply it as soon as you remember, then go back to your usual spacing, and skip it entirely if your next one is almost due. Call a doctor if the sores are not healing by the end of the course, if they spread, or if the area becomes swollen, warm, and oozing pus, which suggests a bacterial infection on top of the herpes lesion.
Side effects to know
- Common: The most common effects are limited to where you apply it and include dry or flaking skin, dry or cracked lips, and a brief burning, stinging, or tingling feeling, and many people notice nothing at all.
- Serious: Stop the product and get medical help right away if you develop hives, widespread rash, or swelling of the face, lips, tongue, or throat, or if you have trouble breathing, since these point to an allergic reaction. Also stop and call a doctor if the treated area develops severe redness, swelling, blistering, or weeping beyond the original sores, which can mean contact dermatitis or a spreading bacterial infection.
Who should not take it?
Do not use acyclovir topical if you have ever had an allergic reaction to acyclovir, valacyclovir, or propylene glycol, which is in the cream base. Tell your clinician if your immune system is suppressed by HIV, cancer treatment, or transplant medicines, because herpes lesions in that setting can spread and usually call for oral or intravenous acyclovir instead of a topical product. Frequent cold sores, genital herpes recurrences, sores that keep coming back in the same place, or an outbreak lasting longer than a week are all reasons to discuss oral antivirals rather than continuing topical treatment. Because so little acyclovir is absorbed through the skin, there are no significant drug interactions with the topical forms, and no alcohol restriction applies. In pregnancy, FDA labeling states there are no adequate and well controlled studies in pregnant women, and clinicians generally consider topical acyclovir acceptable when treatment is needed because systemic exposure is minimal. Acyclovir does pass into breast milk after systemic dosing, so if you are breastfeeding, use it on areas away from the nipple and wash your hands before handling your baby. Do not use it on children younger than 12 for the cream, or younger than 6 for the acyclovir and hydrocortisone combination, unless a clinician directs it.
When is it an emergency?
Serious emergencies with this product are uncommon because very little of the drug reaches the bloodstream. Call 911 if you collapse, cannot breathe, or your face, lips, tongue, or throat begin to swell after applying it. If someone swallows the cream or ointment, call Poison Control at 1-800-222-1222 right away; a full 15 gram tube of 5 percent ointment contains about 750 mg of acyclovir, and swallowing it usually causes at most nausea or vomiting, but Poison Control will tell you whether anything further is needed. If the product gets in the eye, rinse with water for several minutes and call an eye doctor or urgent care, since herpes in the eye is treated differently and needs prompt attention. Seek same-day care if you have a weakened immune system and the sores are spreading quickly, if you develop fever with the outbreak, or if a cold sore is accompanied by a severe headache, confusion, or a new eye problem.
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Common questions
What is the maximum amount of acyclovir cream I can use in a day?
For cold sores, the label sets the limit by number of applications rather than by weight, at 5 applications a day for 4 days. For the 5 percent ointment, the limit is 6 applications a day, roughly every 3 hours, for 7 days. Use just enough to cover the sores, about a half inch ribbon per 4 square inches of skin for the ointment. Applying it more often than this does not speed healing and mostly causes dryness and irritation. If you have finished the course and the sores are still there, call a clinician rather than starting a second round on your own.
Can I drink alcohol while using acyclovir cream or ointment?
Yes. Topical acyclovir is absorbed in very small amounts through the skin, and there is no interaction between alcohol and this medicine. The same is true for oral acyclovir, which also has no alcohol restriction. What is worth knowing is that heavy drinking, poor sleep, and stress are common triggers for cold sore outbreaks in people who get them repeatedly. If your outbreaks cluster around those situations, tracking the pattern can help you start treatment at the first tingle.
Is acyclovir topical safe during pregnancy or breastfeeding?
FDA labeling notes there are no adequate and well controlled studies of topical acyclovir in pregnant women, so it should be used when clearly needed. In practice, clinicians consider it a reasonable option in pregnancy because so little of the drug is absorbed through skin. Acyclovir is known to pass into breast milk after oral or IV dosing, and the amounts after topical use are expected to be very small. If you are breastfeeding, keep the cream off your nipple and areolar area and wash your hands before handling your baby. Tell your obstetric clinician if you have genital herpes in pregnancy, since that is managed differently and often calls for oral antivirals near delivery.
Does it matter whether I take it with food?
No. Acyclovir cream and ointment go on the skin, so food, coffee, and timing of meals have no effect on how well they work. Apply the cream to clean, dry skin and rub it in until it is no longer visible. Do wash your hands before and after each application so you do not carry virus to your eyes or to other people. Avoid putting it inside your mouth, in your eyes, or in the vagina, since these formulations are made for external use.
What happens if someone swallows acyclovir cream or ointment?
Call Poison Control at 1-800-222-1222 right away and describe how much was swallowed. A full 15 gram tube of the 5 percent ointment holds about 750 mg of acyclovir, which is in the range of a single oral dose people take by mouth for herpes treatment, so a one-time ingestion usually causes at most nausea, vomiting, or a headache. Poison Control will tell you whether the person needs to be seen. Call 911 instead if the person is unresponsive, having a seizure, or having trouble breathing. Keep the tube in the box so you can read the strength and the amount to whoever helps you.
Does acyclovir topical interact with my other medicines?
Clinically significant interactions are not expected, because skin absorption is minimal and the drug does not build up in the blood the way oral acyclovir can. Still, list everything you take, including other creams and ointments you plan to use on the same spot, since layering products can increase irritation. If you are on immunosuppressants after a transplant or are receiving chemotherapy, tell your clinician before relying on a topical product, since herpes infections in that situation often need oral or IV acyclovir. And if you already take oral acyclovir or valacyclovir for suppression, ask whether adding the cream gives you anything, because it usually does not.