Medically reviewed by Dr. Ponlawat Pitsuwan, Physician, Takecare Clinic Phuket. Last reviewed: September 2026.
Strong sun on the beach is one of the most common triggers for cold sores that I see in visitors, often on the second or third day of a trip. Starting treatment at the first tingle makes a noticeable difference, so I encourage people with a history of cold sores to travel prepared.
Cold sores are a classic holiday complaint here. Hours on a boat deck, sunlight bouncing off water and sand, wind on the lips, a few late nights and perhaps a cold picked up on the flight all add up, and the familiar tingle starts a few days into the trip. For most people it is a nuisance rather than a danger, but timing makes a real difference to how long it lasts. We also look closely at whether a lip sore is a cold sore at all, because sunburn, impetigo and reactions to lip products can look surprisingly similar.
Why cold sores keep coming back
The World Health Organization estimates that around two-thirds of people under 50 carry HSV-1, usually caught in childhood from a kiss or shared cup. After the first infection, the virus rests in the trigeminal ganglion, a cluster of nerve cells inside the skull that supplies the face, and can reactivate, travelling back down the nerve to the same patch of lip. Ultraviolet light is one of the strongest triggers, which is why beach holidays are notorious. Fever and colds, stress, tiredness, menstruation, chapped or injured lips, and dental or cosmetic lip procedures are others. Some people get a cold sore every year or two, others several times a season, and many carriers never get one at all.
The stages of a cold sore
A cold sore follows a predictable course. Knowing the stage helps you decide what to do, and it shows why the first few hours are so valuable.
| Stage | What you notice | Rough timing | What helps most |
|---|---|---|---|
| Tingle | Tingling, itching or burning at one spot | Hours up to a day | Start antivirals now |
| Blisters | Cluster of small fluid-filled blisters | Days 1 to 3 | Antivirals, a cold sore patch, hands off |
| Weeping | Blisters burst into a shallow sore | Days 3 to 4 | Keep clean, petroleum jelly, most contagious now |
| Crust | Yellow-brown scab that may crack | Days 4 to 8 | Moisturise, do not pick |
| Healed | Scab falls away, skin pink for a while | By about day 10 | Lip sunscreen to prevent the next one |
A cold sore is contagious from the first tingle until it has completely healed, not just while it is weeping.
Is it a cold sore, or something else?
Several lip problems are common in Phuket and are treated differently. Impetigo, a bacterial skin infection, produces golden, honey-coloured crusts that spread quickly and needs antibiotic treatment rather than an antiviral. Mouth ulcers sit inside the mouth on the soft lining, are not contagious and do not start as blisters on the lip. Sunburned lips are swollen, dry and peeling across the whole lip rather than at one spot, and our sunburn treatment page covers them. Cracks at the corners of the mouth are usually angular cheilitis. A new sunscreen, lip balm or toothpaste can cause an itchy, swollen allergic reaction. In children, sores inside the mouth together with spots on the hands and feet suggest hand, foot and mouth disease. Blisters in a band on one side of the face with burning nerve pain may be shingles, which our shingles treatment page describes.
How we treat cold sores
Most cold sores are diagnosed by how they look and how they started. We take a swab for PCR testing only if the picture is unusual, severe, close to the eye, or in someone with eczema or a weakened immune system. Antibiotics do not help a cold sore unless it becomes secondarily infected.
Aciclovir 5% cream, applied about five times a day for five days, gives a modest benefit if started at the tingle and very little once blisters have formed. Antiviral tablets are more effective. Valaciclovir can be taken as a one-day course, famciclovir as a single dose, and aciclovir tablets over five days. Started within the first hours of symptoms, tablets shorten the outbreak and sometimes stop blisters from forming at all. People who get frequent cold sores can keep a prescribed course with them, which is especially useful when travelling. If outbreaks are very frequent, or a known trigger such as a dental procedure is coming up, a preventive course is sometimes appropriate. Hydrocolloid cold sore patches protect the sore, hide it and reduce the chance of spreading the virus with your fingers.
Self-care that is safe while you wait
Leave the sore alone, however tempting it is to pick at the crust. Wash your hands after applying cream, and do not share cups, straws, cutlery, towels or lip balm. Petroleum jelly stops the crust cracking painfully. Paracetamol or ibuprofen help with pain, and a cold, damp cloth soothes the tingle. Salty, acidic and spicy food, such as lime, chilli and sour soups, can sting, so choose milder dishes for a few days. If you wear contact lenses, wash your hands carefully before handling them, because the virus can infect the eye.
Cold sores and oral sex
HSV-1 from a cold sore can pass to a partner’s genitals during oral sex, and it is now a common cause of genital herpes. Avoid oral sex from the first tingle until the sore has fully healed. If a partner develops genital sores after oral sex, our herpes treatment page explains how genital HSV is confirmed and treated, and STD testing in Phuket covers checks for other infections.
When to see a doctor
Most cold sores need nothing more than early antivirals and patience. See a doctor if the sore has not healed after 10 days, if it is very large, painful or spreading, if you get them often, or if you have a weakened immune system because of illness or medication. A red, painful or watering eye, or blurred vision, after a cold sore needs same-day assessment, because herpes can infect the cornea. People with eczema who develop rapidly spreading, painful clusters of sores may have eczema herpeticum, which needs urgent treatment. A child with a first infection may have a mouth full of sores, fever and difficulty drinking.
Prevention and early detection
Because sunlight is such a strong trigger, a lip balm with SPF 30 or higher is the single most useful habit, reapplied after swimming, eating and every couple of hours on the water. A wide-brimmed hat and shade during boat trips help, and so does keeping lips moisturised against wind and salt. Rest after a long-haul flight, drink plenty of water in the heat, and recognise your personal warning tingle so you can start treatment within the hour rather than the next day.
Getting cold sore treatment from us
The sooner antivirals start, the better they work, so our clinics stay open through the night. Walk in to the Bangtao (Cherngtalay) clinic on Bandon Road, the Kata-Karon clinic, or the Patong clinic. You can also message us on WhatsApp with a description of the sore, or telephone +66 81 718 9080. Through our walk-in doctor in Phuket service, most people are seen within minutes, and treatment comes straight from the on-site pharmacy.
For a child with painful mouth sores or anyone unwell with fever, a doctor hotel visit in Phuket is available at any hour. We confirm the price on WhatsApp before your visit. A simple cold sore rarely needs an insurance claim, but if one is severe or needs follow-up, many travel insurers can be billed directly, and we provide an itemised receipt and medical report for everyone else.
Related services and treatments
A cold sore itself carries no HIV risk, but a lip sore sometimes arrives alongside other sexual health questions. After condomless sex in the last 72 hours, PEP treatment in Phuket is the urgent option, while an HIV test in Phuket or our PrEP clinic in Phuket help with longer-term peace of mind. A sore throat after oral sex has several possible causes, including throat infections checked with a swab, as our chlamydia treatment page explains. For women, a change in vaginal discharge after oral sex is more often bacterial vaginosis than herpes, covered under BV treatment. See the full list of conditions we treat for anything else.
Summary
Cold sores are a common reactivation of HSV-1, and Phuket’s sun makes them more likely. Start antivirals at the first tingle, with tablets working better than cream, keep your hands off the sore and do not share lip products. Avoid kissing babies and oral sex until the skin has healed. Seek care for eye symptoms, eczema, a sore lasting more than 10 days or a child who is not drinking.
“If you get cold sores, pack an SPF lip balm and ask us about antiviral tablets before a flare starts. Early treatment at the first tingle works best.”
Dr. Ponlawat Pitsuwan, Physician, Takecare Clinic Phuket
Frequently asked questions
Should I use cream or tablets for a cold sore?
Tablets are generally more effective than cream, particularly when taken within the first hours of the tingle. Aciclovir cream helps a little if applied early and often, and it is a reasonable choice for occasional, mild cold sores. For frequent, painful or large outbreaks, a one-day tablet course of valaciclovir or a single dose of famciclovir usually works better.
How fast can I get antivirals once the tingle starts?
Walk in to any of our clinics and you are usually seen within minutes, with treatment usually dispensed at the on-site pharmacy before you leave. That means treatment can start within the hour, which is when it makes the most difference. If you get cold sores often, ask for a course to keep with you for next time.
Do I need an appointment for a cold sore?
No appointment is needed at any of our three clinics, day or night. Because antivirals work best in the first hours, it is better to come in at the first tingle than to wait for a blister. You can send us a WhatsApp message first if you would like advice on whether a visit is worthwhile.
My child has mouth sores and will not drink. Can a doctor come to our hotel?
Yes. One of our doctors can come to your room, wherever you are staying in Phuket and whatever the hour, to examine your child, check for dehydration and start treatment. A first herpes infection in young children can cause many painful mouth sores, fever and refusal to drink. If your child is drowsy, floppy or has barely passed urine, go to a hospital emergency department or call 1669 instead.
Does travel insurance cover cold sore treatment?
A simple cold sore is usually a quick visit, and some policies have an excess that makes a claim not worthwhile. Severe outbreaks, eye involvement or a child’s first infection are more likely to be covered as a new medical problem. We confirm the price on WhatsApp before your visit and provide a receipt and medical report if you want to claim.
Is it safe to go in the sea or the sun with a cold sore?
Swimming in the sea will not harm the sore or spread the virus, but salt water can sting and sun exposure can slow healing or trigger a second outbreak. Cover the sore with a patch or petroleum jelly, apply SPF lip balm around it, and wear a hat. Avoid sharing snorkels, straws or water bottles until it has healed.
Sources
The NHS page on cold sores explains triggers, treatment and when to get help. MedlinePlus has a clear overview of cold sores and fever blisters. The World Health Organization fact sheet on herpes simplex virus describes how common HSV-1 is worldwide.
Cold sore, herpes labialis, fever blister, herpes simplex virus type 1, HSV-1, oral herpes, prodrome, aciclovir cream, valaciclovir, famciclovir, hydrocolloid cold sore patch, herpetic gingivostomatitis, herpes keratitis, eczema herpeticum, impetigo, angular cheilitis, UV light, NHS, MedlinePlus, WHO, Bangtao, Cherngtalay, Kata, Karon, Patong, Phuket, Takecare Clinic Phuket, Dr. Ponlawat Pitsuwan
This page is general health information and not a substitute for a medical consultation.