The hairs of the oak processionary moth caterpillar can cause skin irritation in humans. In this blog I describe a simple caterpillar dermatitis treatment that stops the itch and pain in less than 30 seconds.
Caterpillar dermatitis is a transient skin condition caused by the irritating hairs of caterpillars. Worldwide there are around 150 species that can cause this red itchy rash. In Europe, the culprits are often the larvae of the oak processionary moth.
The oak processionary moth
The oak processionary moth (OPM, thaumetopoea processionea) has a life cycle of four stages: egg, larva, pupa & moth. The larva is the oak processionary caterpillar. It gets its name from the typical way of travel in nose-to-tail processions, looking for leaves in oak trees on which they feed. Most of their life, they live in and around oak trees. This is also the place where they make their nests to transform into the pupa stage.
Originally the habitat of the oak processionary moth was predominantly Southern and Central Europe. However, due to climate change, the species is now flourishing in Northern European countries like Belgium, the UK and the Netherlands, where there are many oak trees and less natural enemies.
The oak processionary caterpillar has urticating hairs which serve as protection against predators. When these come in contact with human skin they often cause caterpillar dermatitis. One caterpillar can have over 60.000 hairs, which are able to remain active up to 5 years – usually when accumulated in old nests. The hairs can be transported as bio-aerosols by the wind and easily cross a distance of up to 500 meters, while maintaining a relatively high concentration.
Other processionary moths
In the countries that surround the Mediterranean sea there is a related moth that lives on pine trees, known as the pine processionary moth (PPM, Thaumetopoea pityocampa). They also have urticating hairs. Many other varieties of processionary moths are found in Africa, Australia and Madagascar. They feed on pines, oaks and sometimes on cedars and walnut trees. Processionary caterpillars do not occur in North America. Most likely the 30 second caterpillar dermatitis treatment will work for most if not all caterpillars with urticating hairs, including those that don’t walk in nose to tail procession. Let’s now first look at the symptoms of caterpillar dermatitis.
What are the symptoms of caterpillar dermatitis?
The venomous hairs of the caterpillar cause irritation and inflammation. The symptoms depend on which area of the body is affected, and may vary from person to person. See the details hereunder.
Most common is a burning painful sensation or an itchy rash. This can be accompanied by red patches, bumps and blisters. These symptoms will predominantly appear on exposed skin, but can occur on surfaces covered by clothes as well.
In the eyes the hairs cause redness, swelling of the eyelids, itching and watery eyes. It may feel as if there is something in your eye.
If the hairs have been inhaled, one may experience itching or irritation in the nose or throat. This is often accompanied by coughing and a runny nose. Other symptoms can be shortness of breath and difficulty swallowing. If there is a lot of swelling (tongue, lips, throat) this indicates an allergic reaction and a doctor needs to be consulted as soon as possible. In asthma patients the hairs of the oak processionary moth caterpillar can exacerbate asthma attacks.
In case the hairs have been ingested (with food), gastrointestinal discomfort, stomach pain and vomiting may be experienced. also: the mouth may produce a lot of saliva.
Other more general symptoms may be dizziness, headache and fever. People that have had many encounters with the caterpillar hairs may develop a sensitivity over time and become prone to a strong allergic reaction – also known as anaphylactic shock – which can in rare cases be fatal.
What is causing the symptoms?
Caterpillar dermatitis – also known as lepidopterism – is caused by the urticating hairs or spines of the larvae of butterflies and moths. As said, in Europe the oak processionary moth caterpillar is often the culprit. Its fine hairs or ‘setae’ are only around 0.2 millimetres in diameter and can easily penetrate the human skin. Because the hairs are barbed, they easily stick to the skin. The hairs are hollow and filled with the toxic thaumetopoein protein. Once a hair has penetrated, it breaks and releases its allergenic and poisonous contents into the skin. This triggers the release of histamine which causes dermatitis and urticaria.
The combination of a mechanical phenomenon (penetration of hairs which produces irritation) and a chemical phenomenon (the release of thaumetopoein which produces a histamine‐liberating effect) causes the symptoms induced by the oak processionary caterpillar.
The high number of hairs per caterpillar and the transportation as bio-aerosols through the air, explain that symptoms can appear on large surfaces of the body and even at big distances of oak trees.
Once it becomes clear that you are dealing with caterpillar dermatitis, the first step is to reduce harm. Start by moving away from the source to reduce exposure. Do not rub or scratch, as this will only aggravate the symptoms! Then remove the loose hairs from your skin. This can best be done with a piece of adhesive tape. Apply this to the affected area and pull the tape off at once. To remove hairs from the eyes, briefly rinse with lukewarm water. Take off the clothes that have been exposed and wash them at 60 degrees Celcius or more, to inactivate the hairs.
Most of the time doctors will prescribe a cream to treat the affected skin. For mild cases this will be a cooling menthol-based cream. Creams with corticosteroids like triamcinolone acetonide are used to reduce more serious itching and inflammation. For pain caused by caterpillar dermatitis lidocaine or pramocaine creams can are used. There are also creams that combine these ingredients.
For mild allergic skin reactions oral antihistamines, like cetirizine, desloratadine, fexofenadine or loratadine can be prescribed. In severe cases of caterpillar dermatitis – with asthmatic symptoms, angioedema (swelling) or anaphylactic shock – systemic steroids or epinephrine are administered in the hospital.
There are also some over the counter drugs available, like creams with zinc oxide that can protect the skin. Some of the oral antihistamines are also available without a prescription. However, below you will find a 30 sec DIY caterpillar dermatitis treatment that will in most cases make all these pharmaceutical drugs redundant.
THE 30 SECOND CATERPILLAR DERMATITIS TREATMENT
The 30 second caterpillar dermatitis treatment entails heating the skin. This can easily be done in two ways: using a blow dryer or with an infrared heat lamp. Please follow the instructions below.
PREPARATION Before proceeding, take the general necessary steps to reduce harm. Also check the contraindications below. Take off jewellery, watches and glasses as they may be damaged by the heat. Also make sure the skin is dry. Keep some water on hand, to cool your skin in case of overheating. BLOW DRYER Take a blow dryer, switch it on and aim it towards the the affected area of the body. Heat up the skin as much as tolerable for about 20 to 30 seconds, but take care to not overheat. As there may still be some loose caterpillar hairs on the skin, preferably do this outdoors. This way the hairs will not harm you again. INFRARED HEAT LAMP In case you don't have a blow dryer, you can use a wide spectrum infrared heat lamp, like the Philips Infraphil. Place it on a stable surface, switch it on and aim it towards the the affected part of the body. Heat up the skin as much as tolerable for about 20 to 30 seconds, but take care to not overheat. RESULT After the treatment the itch and pain should be gone instantly. The bumps, swelling and redness may take a couple of days to heal.
Risks & contraindications
The 30 sec caterpillar dermatitis treatment is generally safe. Throughout human history heat has been used to enhance health and wellbeing in the form of hot springs, saunas, hammams, sweat-lodges and steam inhalations. Nevertheless, there are some risks & contraindications. Applying heat to the skin may cause burns, if done inappropriately. This may therefore not be a good treatment for young children and animals, as they cannot treat themselves and are less able to judge and communicate their borders. This also applies to people that can’t feel pain or have reduced thermal sensitivity due to illnesses or intoxication (alcohol, drugs). In cases with asthmatic symptoms, angioedema (swelling of the lips, mouth, tongue, eyes) or anaphylactic reaction, always consult a doctor immediately. The blow dryer can remove but may also spread loose urticating hairs – therefore use tape first if you use this method indoors. Be careful with metal piercings as these conduct heat much better than air.
The caterpillar dermatitis heat treatment is primarily to be used by gardeners, foresters, biohackers, doctors, first aiders and other healthcare professionals. Nevertheless, if you are capable and respect the safety precautions, please do try this at home! Be aware that this blogpost article is not personal medical advise, and you do this at your own risk.
Mechanism of the caterpillar dermatitis heat treatment
There are two ways in which the heat of a blow dryer or an infrared heat lamp can reduce the symptoms associated with caterpillar dermatitis. The first is by inactivating the caterpillar’s poison – a protein called thaumetopoein. When exposing the protein to temperatures of above 60 degrees Celcius it will change of structure. This process is called denaturation and causes the protein to loose its allergenic property.
The second way is by increasing blood circulation. This is a known effect of heat therapy and occurs because the body is simply trying to prevent overheating. By increasing vasodilation there is an subsequent increase of the flow of cool blood through the heated area. As a side effect this accelerates tissue healing. Heat therapy is also known as thermotherapy.
There is yet another phenomenon that cannot be ruled out when using an infrared heat lamp. Research in the field of photobiomodulation shows that near infrared light (NIR) has an anti-inflammatory effect. For this to occur the frequency and the dose have to be within certain values. It is unlikely that this plays an important role, because the heat of the lamp will limit the required exposure time.
To my knowledge there are no dedicated scientific studies regarding the use of heat as a therapeutic modality for caterpillar dermatitis so far. However, some studies mention that heat can inactivate the thaumetopoein protein. Like this one from 1983, where the French researchers mention in the abstract that “Heating of this substance (extracted from the hairs) greatly reduced its effects.” Anyway, who needs randomised clinical trials when you can test this safe and virtually free treatment at home in 30 seconds?
How do I know whether my symptoms are caused by a caterpillar?
The diagnosis of caterpillar dermatitis is difficult to make. The symptoms are non-specific and mimic those of other allergic reactions, various dermatological conditions and insect bites. Having been close to oak trees is a clue. There is a detection kit available that is able to identify the oak processionary caterpillar based on DNA from hairs in soil, water and other samples.
Will this treatment also work for dermatitis caused by other caterpillars?
Many European caterpillars – like that of the pine processionary moth – use the same thaumetopoein protein, which will be inactivated by heat. In other regions of the world there are species that use different types of poison, like the giant silkworm moth (lonomia obliqua) in Brazil. This caterpillar has been responsible for many human deaths. I don’t know whether heat can neutralise the poison of this and other caterpillars. However, since heat will deactivate many proteins, it is likely that the 30 second heat treatment can be applied for dermatitis caused by other caterpillars as well.
How about a hot shower?
This may rinse off the hairs, but most likely the highest tolerable temperature of a hot shower – around 40 degrees Celcius – is too low to deactivate the toxin.
What if the hairs are in the eyes?
I have had no personal experience with this, but heat might work in this case as well. Always see a doctor or ophthalmologist first. If no doctor is available or if you are a doctor looking for treatment options, continue reading. There are two problems to tackle: both the mechanical and the chemical irritation of the hairs. The first can to some extent be dealt with by briefly rinsing the eyes with lukewarm water. Important: do not rub, as this may aggravate the penetration of hairs. To neutralise the chemical irritation, use the infrared heat lamp. In case of a 150 Watt lamp use a distance of around 20 cm while keeping eyes closed. Take care not to overheat the eyes! Try this at your own risk. Check this Dutch study (2020) with conventional treatment advice for ocular complications of oak processionary caterpillar setae in the Netherlands. In rare cases serious reduction of vision or blindness can occur, even months after OPM exposure.
What if the hairs got in the airways?
First see a doctor. If no doctor is available or if you are a doctor looking for treatment options, continue reading. In case hairs have been inhaled, going into a hot dry sauna of 80-90 degrees Celcius might work. It may take minutes instead of seconds before the temperature in the throat and lungs rises enough, so stay in there for a while. Realise that the heat can deactivate the thaumetopoein protein, but may not affect the mechanical irritation of the hairs. I have had no personal experience with this application. Please let me know your experiences – good or bad.
Large areas of my body are affected. What now?
Try going into a hot dry sauna of 80-90 degree Celcius for a couple of minutes. This is a full body version of the caterpillar dermatitis heat treatment.
Can I also use the blow dryer to blow the hairs off my skin?
Yes. Do this outside so the hairs will not stay in your environment and cause trouble later.
What if I don’t do anything?
Untreated, mild symptoms will go away by itself within a couple of days to two weeks.
I don’t have a blow dryer or an infrared heat lamp. Can I use something else?
Yes, it is also possible to fill a bottle with hot water (around 70 degrees Celcius) close it and then keep it against the skin. In case you own a bite-away you can use that, but since it treats only a very small surface it will be time consuming.
Can I use my red light therapy LED panel?
No, red or infrared LED devices do not generate enough heat to deactivate the caterpillar toxin. Nonetheless, they can be usefull afterwards for speeding up skin healing.
Heat therapy is an interesting treatment option for caterpillar dermatitis. It is virtually free, produces instant results and has little or no unwanted side effects. If the safety precautions and contraindications are respected there is low risk of harm. Based on my research I conclude that for the majority of mild cases, heat therapy is an effective alternative to pharmaceutical treatment of caterpillar dermatitis.
1. The thaumetopoein protein on Wikipedia (German).
2. Historical overview of research papers on the thaumetopoein protein.
3. The thaumetopoein protein on Chemisty World.
4. Urticating hairs of anials and plants on Wikipedia.
5. Heat Therapy on Wikipedia.
6. Thermotherapy on Physiopedia.
7. Study of the anti-inflammatory effects of photobiomodulation (Hamblin, 2017).
8. Dutch study about climate change and processionary moths.
9. Dutch processionary moth knowledge-platform ‘Kennisplatform Processierups‘.
10. British review studies about OPM exposure.
11. The deadly giant silkworm moth on wikipedia.
12. General OPM info on Dokteronline (Dutch).
13. NHS information about anti-histamines.
14. Airborne hair long-distance transportation study: Dispersion of the bio-aerosol produced by the oak processionary moth
15. First aid video by Emma Hammett.
16. Conventional medical treatments (Dutch).
17. The website and youtube channel of lepidopterist Bart Coppens.
‘The 30 sec caterpillar dermatitis treatment’ was written by Dutch biohacker Tjeerd Verbeek (Biohackz) between July and December 2020. It is being updated irregularly. Find more of his blogposts here.