How To Identify and Treat Buttercup Burn in Horses

Buttercup burn in horses is the sore, red and sometimes blistered skin that appears on pink muzzles, around the lips and on white lower legs after contact with fresh buttercups. Horse & Hound's veterinary adviser Karen Coumbe MRCVS describes it as a contact dermatitis that is worse in wet weather, and warns that the rash can take up to 72 hours to appear. Most cases are mild. In Coumbe's words, "Usually removing affected horses from grazing where buttercups are plentiful will result in a rapid improvement without any drug treatment."

The harder part is being sure it is buttercups. A burnt-looking pink nose can also be sunburn, photosensitisation from liver disease, mud fever, summer sores or something rarer, and some of those need a vet far more than buttercup burn does. This guide covers how buttercup sap damages skin, how to recognise buttercup burn, the look-alikes worth ruling out, how to treat it and how to manage a paddock so it does not come back every summer. If your worry is that your horse has been eating buttercups rather than standing in them, our guide to whether buttercups are poisonous to horses goes deeper into that side of the problem.

What Is Buttercup Burn in Horses?

"Buttercup burn" is a yard name rather than a formal veterinary diagnosis. It describes irritation of sensitive skin where it has touched the sap of fresh buttercups, which belong to the genus Ranunculus. The skin most often affected is the thin, pink skin of the muzzle and lips, and the white skin of the lower legs, because those are the parts that brush through the plants as a horse grazes and walks. The MSD Animal Health Hub puts it simply: buttercups "can cause irritation of the skin they are in contact with (contact dermatitis), particularly of the lower limbs and muzzles of horses."

It is a different problem from buttercup poisoning, which follows eating a large amount of the fresh plant and affects the mouth and gut. The two can turn up on the same overgrazed field, and they share a cause, but the contact form is the one owners meet most. Brinicombe Equine goes further: "Irritation caused by contact with buttercups is far more likely than toxicity from eating them."

How Buttercup Sap Burns: Ranunculin and Protoanemonin

According to Kentucky Equine Research, the leaves and stems of many buttercup species contain ranunculin, a glycoside that forms "the toxic blistering agent protoanemonin" when the plant is chewed or crushed. Protoanemonin is the irritant. On skin it inflames; in the mouth it blisters the lips and raises saliva; further down it irritates the lining of the gut. That is why the same field can give one horse a sore nose and another loose droppings.

Human medicine shows how strong that irritant effect can be. Akbulut and colleagues, writing in the International Journal of Emergency Medicine in 2011, described three patients in Turkey who applied corn buttercup (Ranunculus arvensis) to their skin as a folk remedy for joint pain and developed a phytodermatitis "mimicking burn injury" (PMID 21408003), and reviewed 25 earlier cases. That is people holding crushed plant against their skin, not a horse grazing past the flowers, but it explains why the "burn" in the name is not an exaggeration.

Contact Dermatitis or Photosensitisation?

You will often read that buttercup burn is a reaction to sunlight, and some vets describe it that way: Little Rock Equine Vets in Staffordshire list photosensitisation on pink skin areas among the effects of eating buttercups. Karen Coumbe's account in Horse & Hound is of a contact dermatitis, "worse in wet weather, when moisture on the nose may increase the irritant effect", and she advises that a horse with a serious dermatitis should be checked for other causes, "such as sunburn or photosensitisation."

The reference books do not settle it. The Merck Veterinary Manual (reviewed March 2024) says bulbous buttercup (Ranunculus bulbosus) "has also been presumed to result in hepatogenous photosensitization", and files it under photosensitisation whose cause is not fully understood. The same chapter says liver function "should always be evaluated" in an animal with suspected photosensitisation. For an owner the practical point is the same whichever label wins: the damage sits on the same pink skin, buttercups and strong sun arrive together in early summer, and a burnt-looking nose is worth a vet's look rather than an assumption.

Which Buttercups Grow in UK and South African Paddocks?

Speaking to Horse & Hound, the British Horse Society names meadow, creeping and bulbous buttercups as the varieties owners meet, each "poisonous to varying degrees in its fresh state" and thriving "on poor quality land, old meadows and grassland".

• Creeping buttercup (Ranunculus repens) hugs the ground and spreads by rooting runners, so it can carpet a tired paddock. Kentucky Equine Research notes that buttercups grow best in wet soils, can thrive in heavy clay and are rarely encountered on light, well-drained soil.
• Meadow buttercup (Ranunculus acris) is the tall, branching buttercup of old meadows and hayfields.
• Bulbous buttercup (Ranunculus bulbosus) has a swollen base. The BHS explains that its root holds a number of bulbils "stacked one on top of another", which makes it harder to kill with herbicide. It is also the species behind the most serious equine case report, described below.

In South Africa the widespread native species is the wild or common buttercup, Ranunculus multifidus, known in Afrikaans as botterblom, geelbotterblom or brandblare. The South African National Biodiversity Institute records it in damp grassland, near streams and in marshes in all nine provinces, flowering from September to May. We have not found South African veterinary literature on buttercup burn in horses, so we cannot say how often this species causes it. It is the same genus, and we would apply the same caution to pink noses on damp, buttercup-heavy grazing.

Symptoms of Buttercup Burn in Horses

Buttercup burn shows on the skin that touches the plants while the horse grazes, walks through the field or lies down. The signs to look for are:

• Redness and soreness on a pink muzzle or around the lips. Horse & Hound notes it is often mistaken for sunburn.
• Mild soreness or blistering around the mouth and on the sensitive skin of the muzzle, as Horse & Hound describes it.
• Scabbing as the skin dries. One owner in the 2012 Horse & Hound report described her horse's pink nose being "exacerbated by the buttercups" until it had "gone scabby".
• A rash on white lower legs that looks like mud fever. Brinicombe Equine describes buttercup contact dermatitis as looking "like sun burn on the nose and mud fever on the lower limbs".

Timing matters for spotting it. Because the rash can take up to 72 hours to appear, a horse can come in from a buttercup field looking perfectly normal and show sore skin a few days later, sometimes after it has already been moved. Think back over the last few days of turnout, not just today's field.

Which Horses Get Buttercup Burn?

• Horses with pink skin under white markings. Brinicombe Equine calls the contact dermatitis "fairly common on pink skinned noses and white legs". A broad blaze, a snip over the nostrils, and white socks or stockings all leave pink skin exposed. That includes heavy horses such as the Clydesdale, which often carry a lot of white on the face and legs, and spotted horses such as the Appaloosa, whose mottled skin often leaves pink patches around the muzzle.
• Certain individuals. "Some horses are much more susceptible than others," says Karen Coumbe, and Brinicombe Equine makes the same point: only certain horses react, so the horse that suffers every summer may share a field with several that never do.
• Horses on bare or restricted grazing. Most horses graze around buttercups because they taste bitter. The BHS warns that horses or ponies on overgrazed or restricted grazing may eat them when no other forage is provided, and a horse picking through a buttercup-heavy patch has its nose among the flowers all day.

When Is Buttercup Burn Worst?

Two things drive it: flowering and rain.

• While buttercups are in flower. The BHS says the toxin "reaches its peak during the flowering period", and Brinicombe Equine notes that buttercups in full flower are the most irritant.
• In wet, showery weather. The BHS describes the irritating effects as "further exacerbated in wet weather making showers a riskier period", and Coumbe links it to moisture on the nose increasing the irritant effect.
• In bumper buttercup years. In 2012 RSPCA inspector Kirsty Withnall told Horse & Hound she was receiving more callouts about possible buttercup burn than usual, and earlier in the year. A year later the magazine reported that buttercup burn had been one of the most searched topics on its website.

Signs That It Is More Than Skin Deep

A horse that has eaten a significant amount of fresh buttercup can show signs that go beyond the skin. The MSD Animal Health Hub lists excess salivation, diarrhoea and colic, and notes that the bitter toxin can cause mouth ulcers. Kentucky Equine Research adds blisters on the lips, swelling of the face and diarrhoea that might contain blood. Redwing's vet Nic de Brauwere put it plainly to Horse & Hound: "if eaten, a large amount can also cause diarrhoea and colic."

Protoanemonin works on the lining of the whole digestive system, from the lips down. Drooling, mouth ulcers, colic or diarrhoea are a reason to phone your vet whatever you think the cause is, because none of them is specific to buttercups.

The Severe End: A Kentucky Herd

The most serious equine case on record comes from central Kentucky. Swerczek, writing in the Journal of the American Veterinary Medical Association in 2016 (PMID 26953921), described a herd of Thoroughbreds on spring pastures where bulbous buttercup was "abundantly present in all pastures and paddocks". All the horses lost condition, "especially lactating mares and their foals", even though they were given supplementary grain and hay. Seven mares confirmed pregnant at 30 to 45 days later aborted, and two 2-year-old fillies developed severe diarrhoea, incoordination, recumbency and paralysis and were put down. Post-mortem examination found ulcers and erosions in the stomach and large intestine.

The herd was moved to buttercup-free pasture, all the remaining horses recovered, and the mares that had aborted conceived the following season. Swerczek noted that buttercups had been linked to abortion in cattle but, as far as he knew, never before in horses. This is one farm, one species and an extreme infestation, so it is not a measure of everyday risk. It is a good reason to keep broodmares and foals off pasture where buttercups have taken over.

Do Buttercups Cause Grass Sickness?

You may read that buttercups cause grass sickness. That idea comes from a research group at the School of Pharmacy, University of London. Edwards and colleagues (Frontiers in Pharmacology, 2010, PMID 21833167) sampled 23 grass sickness sites and 11 control sites between March 2007 and September 2008 and found buttercups "in abundance at every EGS site", along with higher soil nitrogen and higher iron, lead, arsenic and chromium in the herbage. Michl and colleagues (Journal of Agricultural and Food Chemistry, 2011, PMID 21842884) then found that buttercups from grass sickness sites differed chemically from control samples.

That is an association, and the authors themselves proposed a multi-factorial cause. The BHS grass sickness page now points to newer work by McGorum and colleagues (2024) identifying a neurotoxic phospholipase A2 enzyme as a possible cause. Buttercups remain a hypothesis, not an established cause. Our guide to grass sickness in horses covers what is known.

Buttercup Burn or Something Else? The Look-Alikes

Karen Coumbe's advice is to look further when a skin problem is serious: "If a horse has a serious dermatitis, check out other possible causes, such as sunburn or photosensitisation." Westgate Laboratories, writing about summer sores, makes the point from the other side: "Don't confuse them with a buttercup burn." This table summarises the conditions most often mistaken for it. Our guide to the most common horse skin diseases covers many more.

Condition	Where it shows	What points to it
Buttercup burn	Pink muzzle, lips, white lower legs	Buttercups in flower in the field, wet weather, improves quickly once the horse is kept away from them
Sunburn	Pink noses and other pink skin under white or grey hair	Strong sun, with or without buttercups in the field
Photosensitisation	Lightly pigmented skin such as the muzzle, eyelids and ears	Horse uncomfortable in sunlight and rubbing; may come with signs of liver disease
Mud fever (pastern dermatitis)	Pasterns and heels	Scabs and matted hair in the heels; a reaction pattern with several possible causes
Summer sores	Lips, face, legs, existing wounds	Round, red, weeping sores that will not heal, sometimes with yellow or white granules
Vesicular stomatitis	Lips, tongue, inside the mouth, snout, feet	Blisters in the mouth; notifiable; never recorded in Great Britain
Sarcoidosis	Often the legs; can be local or widespread	Scaling, crusting and hair loss that persists away from buttercups

Sunburn

The BHS hot weather guidance says horses with pink skin and grey or white hair are the most susceptible to burning, and recommends sun protection "especially on pink noses". The same horses are the ones prone to buttercup burn, so the two often overlap: the 2012 Horse & Hound owner described a pink nose that was "susceptible to sunburn anyway" but made worse by buttercups. One useful clue is the weather. Sunburn follows sunshine, while by Coumbe's and the BHS's accounts buttercup burn is worse in wet, showery spells.

Photosensitisation and the Liver

Photosensitisation is the one look-alike you do not want to miss. The Merck Veterinary Manual for horse owners explains that it happens when light-activated compounds in the skin react with sunlight, that it is "not sunburn, although the difference can be difficult to distinguish", and that the hepatogenous form, linked to impaired liver function, is the more common type in horses. A common cause is grazing plants that damage the liver.

In the UK the best-known example is ragwort, whose pyrrolizidine alkaloids damage the liver: the Merck professional chapter lists them among the toxins that lead to this kind of photosensitisation, and the MSD Animal Health Hub includes sensitivity to sunlight among the signs of chronic ragwort poisoning. St John's wort, by contrast, causes the primary form directly. Nic de Brauwere told Horse & Hound that St John's wort and ragwort are "more worrying" than buttercups. Kopper's 2026 review of liver disease in horses (Veterinary Clinics of North America: Equine Practice, PMID 42276884) lists photosensitisation alongside reduced appetite, weight loss, changes in demeanour, colic, jaundice and diarrhoea. See our guides to ragwort poisoning and removing ragwort from a paddock.

This is why Brinicombe Equine says a vet "will generally take a blood test to ensure the symptoms aren't caused by photosensitivity due to liver disease". A sore nose is a small problem; a sore nose that is the first visible sign of liver damage is not.

Mud Fever on White Legs

On the legs, buttercup burn can look very like mud fever. Yu, writing in Veterinary Clinics of North America: Equine Practice in 2013 (PMID 24267676), describes equine pastern dermatitis as "not a single disease, but a cutaneous reaction pattern", a syndrome rather than a diagnosis, and stresses finding the underlying cause before treating. A contact irritant such as buttercup sap is one possible trigger among several, which is why a leg rash that keeps coming back in early summer, on a horse turned out among buttercups, is worth mentioning to your vet. Our mud fever (pastern dermatitis) entry covers the other causes.

Summer Sores

Summer sores (cutaneous habronemiasis) happen when stomach worm larvae carried by house and stable flies are deposited on moist skin and try to burrow in. Westgate Laboratories describes them as unusual in the UK but becoming more common, and most often found on the lips and face, the legs and any area of damaged skin. The sores are red and raised or open, often greasy-looking with blood-tinged fluid, sometimes containing yellow or white granular material, and on the lips they are often a near-perfect circle. Unlike buttercup burn, Westgate says they are "very unlikely to heal of their own accord without intervention", so a lip sore that does not settle after a move needs a vet.

Blisters Inside the Mouth

Blisters on the lips can come from eating buttercups. Blisters on the tongue, inside the mouth or on the feet are a different matter. Vesicular stomatitis causes "blisters on feet, snout, lips, tongue and inside the mouth" in horses, cattle and pigs, and according to GOV.UK its signs are very similar to foot and mouth disease. It has never been present in Great Britain, but it is a notifiable disease: if you suspect it you must report it immediately to the Defra Rural Services Helpline on 03000 200 301 (in Wales, 0300 303 8268; in Scotland, your local Field Services Office), and failing to do so is an offence. If you see blisters like these, call your vet straight away as well.

Crusting That Will Not Clear

Rarely, scaling and crusting that persists after a horse has been moved away from buttercups turns out to be equine sarcoidosis, an uncommon inflammatory skin disease. In a series of 22 horses from Utrecht, Sloet van Oldruitenborgh-Oosterbaan and Grinwis (Veterinary Dermatology, 2013, PMID 23331701) found the localised form in 68.2% of cases and concluded that sarcoidosis "should be included in the differential diagnosis of a localized exfoliative dermatitis of unknown origin". A 2026 series of 30 equids from Cornell (Garandeau and colleagues, PMID 42399093) found hair loss, crusting and scaling were the most common lesions and the limbs the most affected site. It is diagnosed by biopsy, which is one more reason not to keep treating a non-healing rash as buttercup burn.

How Vets Diagnose Buttercup Burn

Diagnosis is largely circumstantial: there is very little research on buttercups and horses. Coumbe told Horse & Hound that "there is little scientific work on buttercup toxicity, probably as it is considered a low risk", and Swerczek's case report concludes that "on-farm epidemiological investigations are an essential part of the diagnosis". In practice your vet is likely to work through:

1. The history and the field. Whether buttercups are flowering where the horse has grazed, recent weather, recent field moves and whether other horses are affected.
2. Where the lesions are. Skin that touches the plants (muzzle, lips, lower legs) fits contact; Merck notes that photosensitised horses rub lightly pigmented, exposed areas such as the ears, eyelids and muzzle.
3. A blood test for liver function, as Brinicombe Equine describes, to rule out photosensitisation from liver disease. Merck adds that liver enzymes and sometimes a liver biopsy may be needed to confirm liver disease.
4. Further tests if the lesions are atypical or persistent, such as examining material from the wound or a biopsy, which is how summer sores and sarcoidosis are confirmed.
5. The response to moving the horse. "If buttercups are to blame, the condition will rapidly clear if the horse is kept away from the plant for a couple of days," Coumbe told Horse & Hound.

How to Treat Buttercup Burn in Horses

Treating buttercup burn is mostly about removing the cause and protecting the skin while it heals. Work through these steps, and involve your vet early if anything about the case does not fit.

1. Move the horse away from the buttercups. Brinicombe Equine says the best way to solve the problem is to turn the horse out in a different paddock, and points out that because only certain horses react, it may be easier to move the horse than to clear the field. If you have no buttercup-free grazing, our suggestion is to fence off the worst patches with electric tape and to limit a susceptible horse's time in the field during wet spells, when the BHS says the irritant effect is at its strongest.
2. Get the liver question answered. If the skin is more than mildly pink, or anything else about the horse seems off, ask your vet whether a blood test is needed before you treat it as simple buttercup burn.
3. Keep the skin clean and protected. Brinicombe Equine says that once bloods are normal, "applying a barrier cream or leg wraps should protect sensitive skin". Merck advises keeping damaged skin clean to minimise secondary infection.
4. Protect pink skin from the sun. The BHS recommends sun protection on pink noses. If your vet suspects photosensitisation, Merck's advice is stricter: keep the horse fully shaded or, preferably, stabled, and turn out only at night while it lasts.
5. Control flies. Merck warns that damaged skin attracts flies and other insects. A fly mask and repellent protect a healing muzzle, and good fly control also helps prevent summer sores.
6. Leave prescription treatments to your vet. Steroids and antibiotics have a place in some of the look-alikes, but whether a particular horse needs them is a decision for the vet who has seen it. Do not reach for a cream left over from another problem.

If the horse has eaten buttercups and is drooling, off its food, showing colic or passing diarrhoea, call your vet. Mad Barn's veterinary review describes treatment of buttercup poisoning as removing the horse from the contaminated pasture and giving supportive care when signs are severe, and in Swerczek's Kentucky herd every horse that was moved went on to recover.

How Long Does Buttercup Burn Take to Heal?

If buttercups really are the cause, it should not take long. Karen Coumbe told Horse & Hound that "the condition will rapidly clear if the horse is kept away from the plant for a couple of days". Merck describes photosensitisation in a similar way: if exposure to light stops early, the lesions soon resolve, and even badly damaged skin heals remarkably well. A rash that is not clearly improving once the horse is off the buttercups is the most useful warning sign you have that something else is going on, so ask your vet to look again rather than trying another cream.

When to Call the Vet About Buttercup Burn

A mildly pink, slightly crusty nose on a horse you have already moved off the buttercups can usually be watched while it improves. Phone your vet if you see any of the following:

• Skin that is raw, weeping, bleeding, swollen or spreading, or that is not improving once the horse is away from buttercups.
• A horse that seems uncomfortable in sunlight or keeps rubbing its ears, eyelids or face.
• Dullness, a poor appetite, weight loss or a yellow tinge to the gums or the whites of the eyes, which can be signs of liver disease.
• Drooling, ulcers or blisters in the mouth, colic or diarrhoea.
• Blisters on the tongue, inside the mouth or on the feet, because vesicular stomatitis is notifiable.
• Round, red sores on the lips or legs that will not heal.
• Any pregnant mare, foal or youngster grazing a field where buttercups have taken over.

If you are unsure, ring. Your vet would rather hear about a sore nose that turns out to be buttercups than miss the early signs of liver disease.

Preventing Buttercup Burn Through Pasture Management

Buttercups are a symptom of tired grazing. Brinicombe Equine notes that they thrive on the poor soil conditions "so often seen on busy yards", and Kentucky Equine Research warns that, unchecked, buttercup can crowd out other plants, "spreading to cover as much as 40 square feet of ground in a year" (about 3.7 square metres). The long-term fix is a thick, healthy pasture that leaves no gaps for them. Our complete guide to paddock care covers the year-round routine.

Keep the Grass Ahead of the Weeds

• Avoid overgrazing. The BHS says that "improving grass management and preventing overgrazing of pastures" increases the grass sward and reduces the opportunity for buttercups to grow.
• Give hay when grass runs short. Horses on bare or restricted grazing are the ones the BHS expects to turn to buttercups, so put out forage before the field is eaten down.
• Improve the ground. Brinicombe Equine recommends draining, harrowing and aerating to encourage better grass growth. Kentucky Equine Research adds regular soil testing, liming and fertilising, combined with good grazing management and mowing.
• Rest and rotate paddocks so that each field has time to recover before it is grazed again.

Harrow, Dig Out and Top

The BHS says harrowing can be effective at reducing creeping buttercups and that small patches can be successfully dug out. Our guide to grass harrowing explains how and when to do it. Little Rock Equine Vets add that topping fields can help minimise the spread of buttercups and encourage grass growth instead.

Spraying Buttercups Safely

On heavily infested ground a selective herbicide may be the only practical answer. The BHS's advice, given to Horse & Hound, is specific about timing:

• Spray as soon as active growth starts in spring, but before the buttercups flower. Spraying once flowering has started is likely to be unsuccessful.
• Spray when the weeds are dry, make sure no rain is forecast for 12 hours after application, and avoid periods of frost.
• If you miss the spring window, or some plants survive, September is another opportunity.
• Remove horses before spraying and keep them off the pasture for at least two weeks afterwards, or longer if the product label says so.
• Some herbicides require a licence to buy and apply, so the BHS recommends expert advice from a qualified contractor and following the manufacturer's instructions.

Bulbous buttercup is harder to control, because the herbicide may not reach every bulbil in its root and any bulbil that escapes can regrow. The BHS adds that the timing and number of applications needed depend on the species, so a contractor who knows which buttercup you have is worth the call.

Are Buttercups in Hay Safe?

Yes. The BHS says that "in its dried form, buttercups lose their bitterness and toxicity so pose no risk once wilted and included in hay", and the MSD Animal Health Hub agrees that the dried plants in hay are not poisonous. Kentucky Equine Research explains that the toxic oil evaporates quickly after the plants are cut, and adds one catch: buttercup seeds in hay can fall to the ground and start new plants where it is fed. That makes buttercups very different from ragwort, which the MSD Animal Health Hub warns "remains toxic even when the dried plant is incorporated into hay". Our guides to making hay and plants poisonous to horses explain which weeds to keep out of a crop.

Feeding Horses on Poor Pasture

A field covered in buttercups is usually a field short of good grass. Brinicombe Equine points out that such grazing will be fairly poor quality, so horses on little hard feed may not be getting all the vitamins and minerals they need, and a vitamin and mineral supplement or balancer is worth considering.

Buttercup burn is rarely serious, and most horses improve quickly once they are kept away from the flowers. Watch pink noses and white legs closely while buttercups are in flower, especially in wet weather. Move a horse that reacts, let your vet rule out the look-alikes that matter, and work on the pasture over time so the buttercups lose their hold. Do that, and a yellow field can go back to being part of the view rather than a problem.

Frequently Asked Questions