In rare cases, the blisters caused by the herpes simplex virus (HSV) can become infected by other bacteria. If this happens, it could cause a skin infection to spread to other parts of your body, such as the lips, hands or fingers.

In very rare cases, the virus can spread to areas of the body such as the brain, eyes, liver or lungs. People with a weakened immune system are at higher risk of these complications. For example, people with HIV or those using certain medications.

Genital herpes and pregnancy

In some instances, the herpes virus can pose problems during pregnancy and may be passed to the baby around the time of the birth.

Existing genital herpes

If you had genital herpes before becoming pregnant, the risk to your baby is very low. This is because during the last few months of your pregnancy, you will pass all the protective antibodies (proteins that fight infection) to your baby. These will protect your baby during the birth and for several months afterwards.

Even if you have recurrent episodes of genital herpes throughout your pregnancy, your baby should not be at increased risk. However, you may need to take an antiviral medication, such as aciclovir, continuously from week 36 of the pregnancy until the birth to reduce the severity of your symptoms.

If you have genital herpes blisters or ulcers (open sores) at the time of the birth, the chance of passing the infection on to your baby rises to three in 100.   

First and second trimester

If you develop genital herpes for the first time (primary infection) during the first or second trimester, which is up to week 26 of the pregnancy, you may be at risk of having a miscarriage (losing the pregnancy). There is also an increased risk of passing the virus on to your baby.

To prevent this, you may need to take antiviral medicine, such as aciclovir, while you are pregnant.

Third trimester

If you develop genital herpes for the first time during the third trimester (week 27 of the pregnancy until birth), particularly during the last six weeks of the pregnancy, the risk of passing the virus on to your baby is considerably higher. This is because you will not have time to develop protective antibodies to pass to your baby, and the virus can be passed to your baby before or during the birth.

To prevent this happening, you may need to have a caesarean section delivery. A caesarean section is an operation to deliver your baby by making a cut in the front wall of your abdomen (tummy) and womb. If you give birth vaginally, the risk of passing the virus on to your baby is around four in 10.

If you develop genital herpes during the latter stages of pregnancy, you will need to take antiviral medicine continuously for the last four weeks of your pregnancy. However, this may not prevent the need for a caesarean.

Neonatal herpes

Neonatal herpes is where a baby catches the herpes simplex virus around the time of the birth. It can be serious and, in some cases, fatal. However, in the UK neonatal herpes is rare, affecting one or two babies in every 100,000 live births.

There are three types of neonatal herpes that affect different parts of the body. Neonatal herpes can affect:

• the eyes, mouth and skin
• the central nervous system (brain, nerves and spinal cord)
• multiple organs

In babies with symptoms affecting only their eyes, mouth or skin, most will make a complete recovery with antiviral treatment. However, the condition is much more serious in cases where multiple organs are affected and nearly a third of infants with this type of neonatal herpes will die.