Cold sores are tiny painful blisters that can appear on a person’s lips, chin, cheeks or inside their nostrils.
They can also appear on a person’s gums or on the roof of the mouth, although this is less common.
Cold sores are caused by a virus known as HSV-1.
Not everyone who has the virus will get cold sores, and some people may not show any symptoms at all.
Cold sores are very common in New Zealand.
What causes cold sores?
Cold sores are caused by the herpes simplex virus (HSV).
There are 2 types of HSV:
Herpes simplex virus-1 (HSV-1): this is the strand that causes cold sores and fever sores—it can also cause genital herpes.
Herpes simplex virus-2 (HSV-2): this is the strand of the virus that more commonly causes genital herpes
HSV-1 is spread by close contact. Many people catch the virus from the ages of 3–5 when they’re kissed or cuddled by an infected relative.
When a person becomes infected with HSV-1, the virus penetrates their skin and travels along nerve paths to the trigeminal ganglion (a bunch of nerve paths in the inner ear) where it stays indefinitely.
A lot of the time HSV-1 will sit dormant, but when it’s active, the virus travels back along the nerve paths, to the surface of the skin (the epidermis) where cold sores can occur.
Over time, a person’s immune system will start to build up a resistance to the virus and outbreaks will happen less often.
When a person first gets infected with HSV-1, it is called a primary infection:
Some people may not get any symptoms, others will develop blisters, which can be uncomfortable.
The first outbreak usually occurs 1–3 weeks after a person has been infected with HSV-1.
Some people may get blisters inside their mouth—this is known as gingivostomatitis.
When a person has blisters in their mouth and throat, it can make eating and drinking painful and difficult.
After the primary infection, the virus will remain dormant in the nerves until the next outbreak, which has 4 stages:
A tingling sensation in the skin
Minor swelling, which develops into small painful blisters
The blisters cluster and burst creating raw, fluid-filled sores.
After 8–10 days, the sores dry out, scab over and heal completely
Until the sores completely dry out and scab over, they should be considered contagious.
It’s not clear what causes outbreaks of cold sores, but there is an association with:
Being ‘run down’ and unwell, such as when a person catches the flu or a common cold.
Too much sun exposure
When there are only a few blisters, keeping them clean and dry is normally all that’s required for them to heal on their own.
People should be careful not to touch their cold sores if they can help it. If they do, they should wash their hands thoroughly before touching anything else to prevent the virus from spreading.
Picking scabs is a no-no, as this can spread the virus, cause infection or even scarring.
Some people may find that antiviral creams such as aciclovir cream help to speed up the healing, but normally sores will only heal a couple of days faster, and it is only helpful if the cream is used when the ‘tingle’ that precedes blisters first appears.
Pain relief such as paracetamol, ibuprofen or pain-relieving mouthwash (when blisters are inside the mouth) can help to make a person more comfortable.
In really severe cases, antiviral tablets can help decrease the severity of the cold sore outbreak and help it heal up faster.
If blisters or sores become infected, a doctor may prescribe an antibacterial ointment.
Holding ice against the sores may provide some relief.
A clean warm flannel held against the sores may also feel nice, but be sure to wash the flannel afterwards.
Gargling salt water or eating ice blocks may help to relieve blisters inside the mouth.
Common over-the-counter medications
Aciclovir cream, paracetamol, ibuprofen and pain-relieving mouth wash can all be purchased over-the-counter.
How long does a cold sore last?
Once a person has HSV, they have it for life but over time, they should have fewer outbreaks as their body develops a resistance to the virus.
Cold sores usually last about 8–10 days.
Should I see a doctor?
If you develop sores inside your mouth or throat (gingivostomatitis), you should see a doctor. These should really be treated with antiviral medication as well as pain relief.
If your blisters or cold sores become infected, see a doctor as they can prescribe an antibacterial ointment to help.
Most people who have HSV-1 won’t get more than 1 outbreak a year. However, around 5–10% of people will get over 6 outbreaks a year—this is considered a more severe infection and should be discussed with a doctor.
If you get blisters or cold sores near your eyes, see a doctor straight away as infections in the eye can be very dangerous.
Cold sores are considered contagious from the beginning of an outbreak up until the very last sore has healed. To protect yourself against cold sores you should avoid all of the following with anyone who has a cold sore:
Sharing drinks or food
Sharing eating utensils
Sharing lip balm or lipstick
Sharing face creams or sunblock
Sharing towels or face cloths
Letting them touch you after touching their own face
Clinically reviewed by: Dr Mataroria Lyndon
Date of review: 16 December 2021