Aciclovir cream for herpes (cold sore)

This leaflet is for parents and carers about how to use this medicine in children. Our information may differ from that provided by the manufacturers, because their information usually relates to adults. Read this leaflet carefully. Keep it somewhere safe so that you can read it again.

Name of medicine

Aciclovir 5% cream

Common brands: Zovirax

Why is it important for my child to take Aciclovir cream?

Herpes simplex virus causes an infection around the mouth that is commonly known as a ‘cold sore’. Aciclovir slows the growth and spread of the virus so that your child’s body can fight off the infection. It is known as an anti-viral medicine.

What is Aciclovir cream available as?

  • 5% cream: comes in 2 g and 10 g tubes

When should I give Aciclovir cream

Aciclovir cream is usually applied five times a day.

Try to space these times out as evenly as you can. Ideally, around four hours apart.

Apply the cream at about the same time(s) each day so that this becomes part of your child’s daily routine, which will help you to remember.

You must continue using the cream for 3 days after the cold sore has gone.

How much should I give?

Your doctor will work out the amount of Aciclovir cream (the dose) that is right for your child. The dose will be shown on the medicine label.

It is important that you follow your doctor’s instructions about how much to give.

How should I give Aciclovir cream?


  • First, wash your hands thoroughly with soap and hot water.
  • Squeeze a small (pea-size) amount of cream onto the tip of your finger.
  • Spread the cream in a thin layer over the cold sore until it has soaked into the skin. Do not rub the cream/ointment hard into the skin as you may irritate the cold sore.
  • Do not apply the cream to skin that is not affected.
  • Wash your hands thoroughly with soap and hot water after applying the cream.

When should the medicine start working?

The medicine should start working straight away, and your child’s cold sore will start to get better within a few days. Aciclovir works best if it is given as soon as the symptoms appear. The first sign is often a tingling feeling or pain.

It is important to carry on applying Aciclovir cream for a few days after the cold sore has gone. Do not stop early, as the virus may start to multiply again and the cold sore may return. 

What if my child is sick (vomits)?

You do not need to worry if your child is sick, as the medicine will still work.

What if I forget to give it?

Give the next dose as soon as you remember but make sure there is at least 2 hours between each application.

What if I give too much?

It is unlikely to do harm if you give an extra dose of Aciclovir cream or if your child accidentally swallows Aciclovir cream. However, if you are worried, contact your doctor or local NHS services (details at end of leaflet). Have the medicine or packaging with you if you telephone for advice.

Are there any possible side effects?

We use medicines to make our children better, but sometimes they have other effects that we don’t want (side effects).

Side effects you must do something about

If your child is short of breath or is wheezing, or their face, lips or tongue start to swell, or they develop a rash, they may be allergic to Aciclovir cream. Take your child to hospital or phone for an ambulance straight away.

Other side-effects you need to know about

  • Your child’s skin may become red, or may feel itchy or dry. Using a moisturising cream may help
  • Your child may have a stinging or burning feeling where the cream has been applied.

There may sometimes be other side effects that are not listed above. If you notice anything unusual and are concerned, contact your doctor. You can report any suspected side effects to a UK safety scheme at

Can other medicines be given at the same time as Aciclovir cream?

  • You can give your child medicines that contain paracetamol, unless your doctor has told you not to.
  • Check with your doctor or pharmacist before giving any other medicines to your child. This includes herbal and complementary medicines.

Is there anything else I need to know about this medicine?

  • Keep the Aciclovir cream away from your child’s eyes. If your child accidentally gets Aciclovir cream in their eye, wash it out with warm water and contact your doctor if you are worried.
  • It is important that your child completes the course of Aciclovir. This means that you must use the cream for the number of days that the doctor has told you to. Your child’s cold sore will probably heal in a few days, but it takes a few more days for Aciclovir to completely treat the infection. If you stop giving it too soon, the virus may start to multiply again and the cold sore may come back.
  • Aciclovir will not kill all the herpes viruses and some will remain in your child’s body. If symptoms of a cold sore return at any time, which usually starts with a tingling or painful feeling on the skin around the mouth area, get a new prescription of Aciclovir cream from your doctor.

General advice about medicines

  • Try to give medicines at about the same times each day, to help you remember.
  • Only give this medicine to your child. Never give it to anyone else, even if their condition appears to be the same, as this could do harm.
  • Make sure that the medicines you have at home have not reached the ‘best before’ or ‘use by’ date on the packaging. Give old medicines to your pharmacist to dispose of.
  • If you are not sure a medicine is working, contact your doctor but continue to give the medicine as usual in the meantime. Do not give extra doses, as you may do harm.

Where should I keep this medicine?

  • Keep the medicine in a cupboard, away from heat and direct sunlight.
  • It does not need to be kept in the fridge.
  • Make sure that children cannot see or reach the medicine.
  • Keep the medicine in the container it came in.

Who to contact for more information?

Your child’s doctor, pharmacist or nurse will be able to give you more information about Aciclovir cream and about other medicines used to treat herpes simplex infection.

England: NHS 111

Tel 111

Scotland: NHS 24

Northern Ireland: NI Direct

Wales: NHS 111 Wales

Copyright disclaimer

Version [2]. © NPPG, RCPCH and WellChild, all rights reserved. Review by April 2022.

The primary source for the information in this leaflet is the British National Formulary for Children. For details on any other sources used for this leaflet, please contact us through our website,

We take great care to make sure that the information in this leaflet is correct and up-to-date. However, medicines can be used in different ways for different patients. It is important that you ask the advice of your doctor or pharmacist if you are not sure about something. This leaflet is about the use of these medicines in the UK, and may not apply to other countries. The Royal College of Paediatrics and Child Health (RCPCH), the Neonatal and Paediatric Pharmacists Group (NPPG), WellChild and the contributors and editors cannot be held responsible for the accuracy of information, omissions of information, or any actions that may be taken as a consequence of reading this leaflet.