On this page
Dr. Chrysoula I. Liakou MD, PhD
- Treated online: Yes, for itchy rashes and mild eye or throat irritation; breathing difficulty or a severe allergic reaction needs 112.
- The cause: tiny hairs on processionary caterpillars and their nests, which break off and release an irritating protein called thaumetopoein. The wind can carry them.
- When: oak processionary caterpillars are most risky from May to July; pine processionary caterpillars cause most reactions from February to April.
- The rash: itchy red bumps and welts on exposed skin, such as the neck, wrists, forearms and ankles, usually within hours of contact.
- Emergency: call 112 for swelling of the lips, tongue or throat, difficulty breathing, or feeling faint.
Do not book a video appointment if, after contact with caterpillars or their nests, you have swelling of the lips, tongue or throat, wheezing or difficulty breathing, or feel faint: call 112. Hairs in the eye that cause severe pain, blurred vision or sensitivity to light need urgent in-person eye care.
Can an online doctor treat a caterpillar rash?
Yes. A caterpillar rash is recognised by how it looks and by where you have been, and a doctor can assess it by video, along with any eye, nose or throat symptoms. The doctor can ease the itching and inflammation with tablets or creams and tell you how to avoid the next reaction. Breathing difficulty or a severe allergic reaction needs 112, and an injured eye needs in-person care.
How an online consultation helps with a caterpillar rash
- The cause identified: A rash after time under oak or pine trees, often without touching a caterpillar, points to their hairs.
- Eyes and breathing checked: The doctor checks for eye irritation, a sore throat and breathing problems, not only the skin.
- Relief that suits you: Antihistamine tablets, a steroid cream or, for a severe rash, steroid tablets, chosen after the doctor checks your other medicines.
- The next reaction avoided: Repeated contact can make reactions stronger, so the doctor helps you plan how to avoid the hairs.
What the doctor checks in an online caterpillar rash consultation
The doctor checks your breathing and eyes first, then the skin. The doctor asks about:
- Warning signs: swelling of the lips, tongue or throat, wheezing, breathlessness or feeling faint.
- The rash: where it is, when it started, and whether it is spreading.
- Your eyes: pain, redness, watering, blurred vision, or a feeling of something in the eye.
- Nose, throat and chest: a runny nose, a sore throat or a cough.
- The contact: oak trees, pine woods, parks or gardens, caterpillars or nests, the time of year, and your pets.
- Your health: asthma and other allergies, pregnancy, and the medicines you take.
Before the call, rinse the skin, photograph the rash in good light, and note where and when the contact may have happened.
How do processionary caterpillars cause a rash?
Processionary caterpillars are covered in tiny hairs. The hairs have spines that break off and release a protein called thaumetopoein, which triggers the release of histamine in the skin and causes inflammation. You do not have to touch a caterpillar: hairs reach people who brush past an infested tree, and the wind carries them from nearby trees. Old nests keep their hairs for months, so reactions are possible at any time of year.
Swipe sideways to compare →
| Where | What you may notice | How soon |
|---|---|---|
| Skin | Itchy red bumps, scratch marks and eczema-like patches on exposed skin | Within hours, lasting several days |
| Skin, allergic | Raised, itchy welts, sometimes with swollen eyelids | Soon after contact, settling within hours |
| Eyes | Red, itchy, watering eyes; rarely, hairs injure the eye itself | Soon after contact |
| Nose, throat and chest | A runny nose, a sore throat, and occasionally breathing difficulty | Soon after contact |
| Whole body | Rarely, a severe allergic reaction | Usually within an hour |
Repeated contact can make you more sensitive, so later reactions can be stronger.
Oak and pine processionary caterpillars
Two processionary moths cause most caterpillar rashes in Europe:
Swipe sideways to compare →
| What differs | Oak processionary | Pine processionary |
|---|---|---|
| Where | Oak trees in parts of central Europe and in England | Pine trees, mainly in Mediterranean countries |
| When caterpillars are out | They emerge from late March to May; greatest risk from May to July | Processions down the trees in early spring; most reactions from February to April |
| Nests | Dome or teardrop-shaped silk nests on oak trunks and branches, white at first, then brown | Silk nests in the branches of pine trees |
| Hairs | Develop when the caterpillars reach about 1 cm | Remain in the environment all year round |
In one population study in Spain, 12% of people in rural areas had reacted to pine processionary caterpillars, against 4.4% in urban areas, and forestry workers had about five times the risk.
How to recognise oak processionary caterpillars and nests
Oak processionary caterpillars are easiest to spot in late spring and early summer, when they move in lines and build their nests:
- Caterpillars: black heads and grey bodies covered in long white hairs. They are about 2 mm long when they hatch in spring and grow to 2 to 2.5 cm, and they travel nose-to-tail in a procession.
- Nests: dome or teardrop-shaped, from the size of a golf ball to a rugby ball, on oak trunks and branches at any height. They are white with silky trails at first, then turn brown, and stay on the tree for many months. Old nests are easiest to see in winter, when the leaves have fallen.
- Moths: brown, with a wingspan of 25 to 35 mm, alive for only a few days in mid to late summer. The irritating hairs come from the older caterpillars.
- Look-alikes: other caterpillars, such as the cotoneaster webber and small ermine moths, also spin webbing on trees and hedges, and they are harmless.
Where oak processionary moth is found in England
Oak processionary moth was first identified in London in 2006 and has spread to some surrounding counties in south-east England. England is divided into an established area, where the moth is known to be present, a buffer zone around it, and a pest-free area covering most of the country. It is a regulated quarantine pest, and landowners in the established area are responsible for managing it on their land.
What to do after contact with caterpillar hairs
- Move away from the trees, caterpillars or nests.
- Rinse the skin with plenty of water, without rubbing.
- If your eyes sting, rinse them with clean water and do not rub them.
- Change your clothes, and wash them before you wear them again.
- Ask a pharmacist about antihistamine tablets for the itching. Do not use an antihistamine cream after contact with caterpillar hairs.
- If you see a doctor or a vet, say that you suspect processionary caterpillars.
Do not scratch: scratching breaks more hairs and releases more of the irritant.
Which caterpillar rash treatment might the doctor recommend?
Treatment depends on where the hairs have caused a reaction and how strong it is. This is the framework the doctors use:
Swipe sideways to compare →
| What you have | Likely first step | Suitable for online care? | When in-person care is needed |
|---|---|---|---|
| Itchy bumps or welts on exposed skin | Antihistamine tablets and cool compresses | Yes | Not usually needed |
| A widespread or eczema-like rash lasting days | A steroid cream, sometimes steroid tablets | Yes | Not usually needed |
| Red, itchy, watering eyes | Rinsing, and an assessment of the eyes | Yes, to assess | If pain, blurred vision or light sensitivity |
| A sore throat, runny nose or cough | An antihistamine, and an assessment | Yes, to assess | If breathing becomes difficult |
| A reaction every time you are near the trees | An allergy assessment and a plan to avoid the hairs | Yes | For allergy tests |
| Swelling of the lips, tongue or throat, or difficulty breathing | Adrenaline and emergency treatment | No | Call 112 now |
Not sure whether a rash came from caterpillars? A doctor can look at it on camera in one consultation.
See available times →Treatment options for a caterpillar rash
What you can do yourself
- Rinse the skin and change your clothes after contact.
- Take an antihistamine tablet for the itching.
- Hold cool compresses on itchy skin, and do not scratch.
- Keep away from the trees where the reaction started.
Prescription treatment
A prescription is never issued without a consultation. For an inflamed, eczema-like rash, the doctor may prescribe a steroid cream, and for an extensive or persistent reaction, a short course of steroid tablets. Severe allergic reactions are treated with adrenaline. If the doctor prescribes, use the prescription at a pharmacy near you.
What does not help
Scratching or rubbing, which releases more of the irritant. Antihistamine creams, which are not recommended after contact with caterpillar hairs. Touching nests, or trying to remove them yourself.
How to avoid caterpillar hairs
- Do not touch or go near the caterpillars or their nests, and keep children and pets away from them.
- Avoid infested pine woods during the procession season, and wear clothing that covers the skin in affected areas.
- Leave nests to professionals: removing them is hazardous.
- In England, report oak processionary moth nests or caterpillars through the TreeAlert service, including empty nests, and tell neighbours with oak trees, who may have them too.
If you find a nest in your garden, do not touch it, keep children and pets away, and use a specialist contractor to remove it. The greatest risk is from May to July, but hairs left in old nests can cause reactions at any time of year.
Special situations
Dogs and other pets
Dogs pick up hairs on their paws and in their mouths by sniffing or licking caterpillars and nests. A pet with a swollen tongue or mouth needs a vet urgently.
Tree surgeons, gardeners and forestry workers
Regular contact raises the risk of strong reactions. Protective clothing and eye protection matter, and allergy tests can help if reactions keep getting worse.
Pregnancy
Tell the doctor if you are pregnant, because it changes which antihistamines and steroid treatments are suitable.
Children
Mobi Doctor consultations are for adults aged 18 and over. A child who is unwell needs a paediatrician or a local doctor in person, and emergency signs in a child mean 112.
When a caterpillar rash is treated online, and when you need in-person care
Treated online: itchy rashes and welts, eczema-like reactions, mild eye or throat irritation, and advice on avoiding the hairs.
In-person care: breathing difficulty, swelling of the lips, tongue or throat, eye pain or blurred vision, and allergy testing.
When to get in-person care
Call 112 or go to an emergency department now for:
- swelling of the lips, tongue or throat
- wheezing, breathlessness or difficulty breathing
- feeling faint, confused or collapsing
- a widespread rash with feeling very unwell
Get medical advice the same day for:
- eye pain, blurred vision or sensitivity to light after contact
- a feeling of something stuck in the eye that does not wash out
- a rash that is spreading or blistering, or that keeps you awake
- a cough or a sore throat that is getting worse
How Mobi Doctor works
- Book a time that suits you: daily 7am–11pm CEST. You can see a doctor over video, usually within 15 minutes. No subscription, and the exact price is shown before you pay.
- Speak to a licensed doctor about the rash: show it on camera in good light, and say where you had been, when it started, and whether your eyes or throat are affected.
- Leave with a plan: what to do, what to take and for how long, and which signs mean you should be seen in person. If the doctor prescribes, use the prescription at a pharmacy near you.
No sign-up needed
Not sure it’s a caterpillar rash? Tick every symptom you have to see each condition page that mentions it. It finds the right page, not a diagnosis: a doctor gives you that on a video call.
Tap the body — an area or a point — to browse symptoms anywhere
Similar symptoms, different condition? Contact dermatitis can start the same way. Compare them, or look up any other symptom in the full symptom checker.
Frequently asked questions about caterpillar rash
What does an oak processionary moth rash look like?
A caterpillar rash from the oak processionary moth shows itchy red bumps, scratch marks and sometimes raised welts on exposed skin, such as the neck, wrists, forearms and ankles. It usually appears within hours of contact and lasts several days.
Can you get a caterpillar rash without touching a caterpillar?
Yes. The caterpillar hairs break off and are carried by the wind, and they stay in old nests for months. People react after brushing past infested trees or standing near them.
How long does a caterpillar rash last?
The itchy bumps usually last several days. Raised welts from an allergic reaction settle within hours. A doctor can prescribe treatment if the rash is severe or lasting.
When are processionary caterpillars dangerous?
Oak processionary caterpillars are most risky from May to July, and pine processionary caterpillars from February to April, when they come down the trees in processions. Hairs remain in nests, so reactions can happen at any time of year.
What should I do at home after touching a processionary caterpillar?
Move away from the caterpillars, rinse the skin with water without rubbing, rinse your eyes if they sting, change your clothes, and take an antihistamine tablet. Do not use antihistamine cream, and do not scratch.
Are processionary caterpillars dangerous to dogs?
Yes. Dogs get hairs on their paws and in their mouths, and their tongue and mouth can swell. A dog that has touched caterpillars or a nest needs a vet promptly.
Can caterpillar hairs affect your eyes?
Yes. Caterpillar hairs often cause red, itchy, watering eyes. Rarely, hairs damage the eye itself, so eye pain, blurred vision or light sensitivity needs urgent in-person care.
Can processionary caterpillars cause breathing problems?
Occasionally. Breathing in the caterpillar hairs can cause a runny nose, a sore throat and, rarely, breathing difficulty or a severe allergic reaction, which needs 112.
What do oak processionary caterpillars look like?
Oak processionary caterpillars have black heads and grey bodies covered in long white hairs, grow to about 2 to 2.5 cm, and move nose-to-tail in a procession. Their nests are white, then brown, silk domes on oak trunks and branches.
Do you have to report oak processionary moth?
In England, yes: sightings of the caterpillars or nests, including empty nests, are reported to the Forestry Commission through the TreeAlert service. Do not touch or remove them yourself.
Where is oak processionary moth found in the UK?
The oak processionary moth is found in London, where it was first identified in 2006, and in some surrounding counties in south-east England. Most of the country is a pest-free area, where any sighting leads to action to remove it.
Is it a caterpillar rash or something else?
A caterpillar rash is easy to mistake for insect bites, hives or eczema, because the itchy welts and bumps look alike. The clue is where you have been: a rash that appears after time under oak or pine trees, often without touching a caterpillar, points to processionary caterpillar hairs. Oak processionary caterpillars are out from late March to May, with the greatest risk from May to July; pine processionary reactions are most common from February to April.
Can an online doctor treat a caterpillar rash?
Yes, for itchy rashes and mild eye or throat irritation. A doctor can assess the reaction by video and prescribe treatment. Breathing difficulty or swelling of the lips, tongue or throat needs 112.
- Managing oak processionary moth in England, Forestry Commission, UK Government, updated 13 August 2026.
- Skin reactions on exposure to the pine processionary caterpillar (Thaumetopoea pityocampa), Vega J, Vega JM, Moneo I. Actas Dermo-Sifiliográficas, 2011.
- Pine processionary caterpillar, Thaumetopoea pityocampa, contact as a health risk for dogs, Kaszak I et al., Annals of Parasitology, 2015.
- Insect bites and stings, NHS, National Health Service (UK), reviewed 1 June 2023.
- Oak processionary moth, RHS, Royal Horticultural Society, 2026.
This page is for information only and is not a substitute for a medical consultation. Guideline links are provided for transparency; treatment decisions are made with your doctor.
Related conditions
Related reading from the Mobi Doctor blog
Speak to a doctor about a caterpillar rash over video, usually within 15 minutes
Licensed doctors · open daily 7am–11pm CEST · exact price before payment
See available times →