Herpes simplex virus type 1 (HSV-1): cold sores and what to know

There are two herpes simplex viruses. HSV-1 usually causes infection around the mouth, lips, cheeks or nose, which is called herpes labialis or a cold sore. The NHS says most people are exposed to the virus as children, through close skin-to-skin contact such as kissing someone who has a cold sore.

NICE CKS adds that most HSV-1 infections cause no symptoms at all, and that a symptomatic first infection often shows as gingivostomatitis, painful sores in the mouth and gums, in children. The virus is transmitted through direct contact with infected secretions from a person who is actively shedding virus.

The NHS says a cold sore usually starts with a tingling, itching or burning feeling, and that over the next 48 hours one or more painful blisters appear on the face, usually small and filled with fluid. They burst and crust over into a scab. NICE CKS says this early warning lasts typically 6 to 48 hours before lesions show, and that they usually heal without scarring.

Not every sore on the face is a cold sore. The NHS lists a spot or boil (a painful red spot filled with pus), a mouth ulcer (a blister on the inside of the lip or mouth) and impetigo (red sores that become crusty, golden-brown patches) as other possibilities.

After the first infection the virus stays dormant in the skin and can reactivate. The NHS names illness, sunshine and being on your period as triggers; NICE CKS names ultraviolet light, stress, fever and trauma to the area. The NHS advice is to avoid triggers where you can, such as sunbeds, and to use a sunblock lip balm of SPF 15 or above when out in the sun.

A pharmacist can recommend creams to ease pain and irritation, antiviral creams to speed healing, and cold sore patches to protect the skin. The NHS says that if you regularly get cold sores, antiviral creams should be used as soon as you recognise the early tingling, since they do not always work after blisters appear. Electronic devices that treat cold sores with light or lasers are sold, but the NHS says there is not much evidence that they work. NICE CKS notes that topical treatments are not routinely recommended but some people find them helpful.

• Take paracetamol or ibuprofen for pain and swelling (liquid paracetamol is available for children); the NHS says not to give aspirin to children under 16.

• Drink plenty of fluids to avoid dehydration.

• Do not touch the sore except to apply cream, and wash your hands before and after.

• Dab cream on rather than rubbing it in.

• Avoid acidic or salty food if it makes the sore feel worse.

Cold sores spread easily to other people and to other parts of your body. The NHS advises washing your hands with soap and water whenever you touch the sore, not kissing anyone while you have one, and not having oral sex until it heals completely, since you could give your partner genital herpes. A cold sore that touches the genitals can cause genital infection.

The NHS highlights babies as the group at greatest risk, because kissing a baby can lead to neonatal herpes.

The NHS says to see a GP if a cold sore has not started to heal within 10 days, you are worried or think it might be something else, it is very large or painful, you or your child also have swollen, painful gums and sores in the mouth, or you have a weakened immune system, for example from chemotherapy or diabetes. A GP may prescribe antiviral tablets if the cold sores are very large, painful or keep coming back. Newborn babies, pregnant women and people with a weakened immune system may be referred to hospital.

NICE CKS warns that oral HSV can cause severe or life-threatening complications, especially in people with weakened immunity. These include eczema herpeticum, eye disease with corneal ulceration, erythema multiforme, pneumonia and encephalitis. A painful red eye, sore spreading rash on skin affected by eczema, or confusion with fever needs urgent medical help; use NHS 111 or call 999.

HSV-1 is not limited to the mouth. NICE CKS states that HSV-1 is the most common cause of both oral and genital herpes in the UK, with HSV-2 more likely to cause recurrent genital herpes. Genital HSV-1 can follow oral sex with someone who has HSV-1, which is one reason the NHS advises avoiding oral sex while a cold sore is present.