What are scratches (mud fever), and how do I prevent them?

UF/IFAS Extension lists the other names as mud rash, greasy heel and dew poisoning, and calls it equine pastern dermatitis. University of Minnesota Extension says "scratches" can refer to several skin conditions in that area.

That last point matters. Scratches describes what the skin looks like; it is not one disease with one cause. So this page can tell you what sources say about why it happens and how horse owners lower the risk. It cannot tell you what is going on with your horse's legs. Your vet can.

University of Minnesota Extension names prolonged moisture, such as a muddy field or a wet stall, as the main trigger: constant wetness irritates delicate skin, and mud and dirty surroundings then let bacteria or fungi in. UF/IFAS Extension says wet conditions weaken the skin's barrier, and that recent rain and morning dew keep the environment wet. It adds that abrasive grasses and sun exposure have been implicated, but that the full range of contributing factors isn't fully understood.

The University of Kentucky's Equine Disease Quarterly lists more: dirt, manure, wetness, chemical irritants, UV light and trauma such as plant stubble, rocks, or a horse overreaching or interfering. Teagasc, the Irish agriculture and food authority, says bacteria are most often the cause, and that leg mites, which break the skin, are another, particularly in horses with thick feathers. It also lists wounds, long periods standing in mud or dirty bedding, and frequent leg washing as ways the skin gets damaged. The Horse reports that the Merck Veterinary Manual says no specific cause is known, though the condition is often associated with poor stable hygiene.

UF/IFAS Extension says it is most common in horses with long pastern hair, which can hold moisture, and in horses with nonpigmented skin such as white leg markings. Teagasc lists white legs with pink skin, and says feathered horses are at higher risk of leg mites. The Horse adds that, per Merck, heavy horses are particularly susceptible and the hind legs are affected more often. The Equine Disease Quarterly says draft breeds are more prone, likely because of heavy feathering and possibly genetics.

Immune health comes up too. Teagasc lists a weakened immune system, for example from Cushing's disease, as a predisposing factor, and says to involve your vet if you suspect it. If a horse gets scratches again and again, or it won't clear, that is a reason to ask your vet what is underneath it.

UF/IFAS Extension describes early redness, scaling and swelling, then oozing, matted hair, hair loss, crusting and thickened skin, usually around the hind pastern or fetlock and sometimes the heel bulbs. Untreated lesions can spread to the front of the pastern and fetlock, and the skin can be itchy and painful.

Teagasc adds creamy, white, yellow or green discharge under scabs, and heat, pain and swelling in the lower limb, with lameness in severe cases. University of Minnesota Extension calls heat, swelling and pain in the leg a sign of a more serious infection, and UF/IFAS says severe cases can reach deeper tissue and cause cellulitis.

Other skin problems can look similar. Teagasc says rain scald, which puts scabs along the neck, back and hindquarters, can resemble mud fever, and that a vet check can rule out ringworm. That is one more reason to have a vet look rather than guess.

The table collects what the extension and agency pages we read suggest. Your vet can tailor it to your horse.

Teagasc says to check limbs daily to spot signs early, and UF/IFAS Extension says regular grooming helps maintain skin health and catch irritations early. The list below is built from the signs those pages and University of Minnesota Extension describe.

The point of a routine is that early changes are easy to miss in a coat that is thick, feathered or caked with mud. Teagasc's advice to let mud dry and brush it off means you can see the skin without scrubbing it. If you find something, don't treat it yourself. Write down what you see and when, and ring your vet.

• Redness, scaling or swelling on the back of the pastern or the heel bulbs.
• Scabs or crusts, matted hair, or patches where hair has come away.
• Any discharge under scabs.
• Heat, swelling or pain in the lower leg, or lameness.
• Anything that looks different from the day before, or from the other legs.

University of Minnesota Extension says to clean hobbles, boots and wraps thoroughly before reuse. UF/IFAS Extension doesn't address boots or wraps, and Teagasc doesn't list leg protection among its prevention steps. So the honest answer is that we found no vet or extension source saying either way. Ask your vet about your horse, especially if she already gets scratches.

Riders do use boots, and one rider's experience is below. It is one rider's account, not a recommendation, and she makes the same point the sources do about keeping things clean and dry. Our page on what each kind of horse boot is designed to do covers the styles, and our hoof boot page covers boots for the foot itself.

UF/IFAS Extension says to call your vet if you suspect scratches, because a vet can examine the legs, run tests to find the underlying cause and recommend treatment. Teagasc says to involve a vet as soon as mud fever is suspected, and again if mites are suspected, if signs could be ringworm or rain scald, if it isn't clearing, or in severe cases. University of Minnesota Extension says severe cases are usually treated with a vet-directed prescription cream, and the most severe may need a course of oral antibiotics.

Why not try something at home first? Because the cause decides the treatment. The Equine Disease Quarterly says a vet's routine workup can include cytology, skin scrapings, hair microscopy and fungal cultures, with biopsy reserved for severe or unresponsive cases, and that early, correct diagnosis can greatly speed resolution. That piece dates from 2013, so ask your vet what current practice is. Both University of Minnesota Extension and UF/IFAS say not to pick off scabs; UF/IFAS says to soften crusts by washing the legs.

If the leg is hot, swollen or painful, or your horse is lame, call your vet promptly rather than waiting to see if it settles.