Rain Scald (Dermatophilosis)
Learn what the condition is, how it may be detected early, how it is treated or managed, and which breeds or species are linked to it.
Condition snapshot
A concise guide to the condition’s pattern, detection, management and urgency.
This snapshot is a general guide, not a diagnosis or treatment plan. New, severe or worsening signs require veterinary assessment.
About the condition
Rain scald is superficial bacterial skin infection caused by Dermatophilus congolensis. The organism can persist quietly on skin and becomes invasive when prolonged rain, humidity, dense wet coat, insects or minor trauma disrupt the epidermal barrier. It is common along the back, rump and neck where rain runs, while lower-limb disease is sometimes called mud fever or strawberry foot.
Characteristic tufts of matted hair lift with crusts, producing paintbrush-like clumps and moist pink skin beneath. Lesions can be tender or itchy. In a short coat, small scaly patches may replace obvious thick scabs. Severe generalised disease causes pain, weight loss and reduced movement, especially in young or immunocompromised horses.
The condition can spread by direct contact, insects and contaminated rugs, tack or grooming tools, although moisture is often necessary for clinical disease. It is distinct from ringworm, which is caused by dermatophyte fungi and often spreads in circular areas, but appearance overlaps enough that microscopy is useful. Dermatophilus can rarely infect people through damaged skin.
Most cases heal without scarring once the horse is dry and infection is treated. Failure to improve suggests continued wetting, an underlying immune or nutritional problem, incorrect diagnosis or deeper bacterial infection. Pulling firmly attached crusts without soaking is painful and creates more barrier damage. A horse with fever, deep limb swelling or severe lameness has disease beyond routine rain scald and needs urgent reassessment.
Dermatophilus congolensis proliferates when prolonged wetting disrupts the skin barrier. Tufts of hair lift with paintbrush-like crusts, leaving moist pink skin beneath. It is not simply rain exposure: tack friction, dense coats, poor shelter and immune compromise change susceptibility, and shared equipment can mechanically transfer organisms between horses.
Dry conditions halt bacterial motility and help the intact barrier recover.
Screening & Early Detection
The distribution, wet-coat history and paintbrush crusts raise suspicion. Fresh crust undersides or impression smears are examined microscopically for branching rows of coccoid organisms. Cytology also shows inflammation and secondary bacteria. Culture can assist atypical or severe cases but the organism may be difficult to recover after topical treatment.
Dermatophyte culture or PCR, skin scraping and biopsy are used when ringworm, mites, bacterial folliculitis, pemphigus or another scaling disease remains possible. Generalised or recurrent infection justifies blood testing and assessment for PPID, malnutrition or immunosuppression. Pastern lesions are evaluated for cellulitis and other causes of pastern dermatitis.
Affected horses are separated and given dedicated grooming equipment while diagnosis is resolved. Owners should inspect under rugs rather than assuming a waterproof cover kept the coat dry; sweating and trapped moisture can sustain disease. Lesion counts and photographs document response after environmental correction.
Cytology from the underside of a fresh crust can reveal the characteristic branching coccoid organisms. The horse's temperature and general health are checked when lesions are widespread or unexpectedly painful.
Treatment & Management
The horse is moved to a dry, well-ventilated area and wet rugs removed. Crusts are soaked gently and loosened without tearing viable skin. Antimicrobial shampoo, commonly chlorhexidine, is worked into affected areas and rinsed or left according to product direction, then the coat is dried completely. Infectious crust material is bagged and discarded rather than brushed around the stable.
Extensive, painful or systemic disease may require veterinarian-selected systemic antibiotics. Secondary cellulitis is treated aggressively. Clipping improves access in a long coat only when it can be performed without traumatising inflamed skin. Anti-inflammatory medication supports comfort in severe cases.
Rugs, brushes, tack and clippers are cleaned of organic material before appropriate disinfection; fabric is laundered and dried. Handlers wear gloves and wash hands. Horses stay separated until active lesions resolve, particularly in shared facilities. Long-term prevention keeps coats dry, avoids sharing equipment and manages biting insects. Waterproof rugs are checked for leakage and sweat accumulation. Improvement should be apparent within days and most uncomplicated lesions heal over two to three weeks.
Shared rugs and brushes remain out of service until cleaned and fully dried.
Breeds or species affected
Akhal-Teke
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Anglo-Arabian
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Arabian
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Barb
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Caspian
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Kathiawari
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Marwari
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Shagya Arabian
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Thoroughbred
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American Quarter Horse
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American Paint Horse
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Appaloosa
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Australian Stock Horse
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Brumby
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Waler
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Morgan
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Standardbred
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American Saddlebred
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Tennessee Walking Horse
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Missouri Fox Trotter
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Rocky Mountain Horse
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Peruvian Paso
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Criollo
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Mustang
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Canadian Horse
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Andalusian
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Lusitano
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Lipizzaner
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Friesian
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Dutch Warmblood
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Hanoverian
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Holsteiner
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Oldenburg
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Westphalian
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Trakehner
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Selle Français
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Belgian Warmblood
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Danish Warmblood
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Swedish Warmblood
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Swiss Warmblood
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Australian Warmblood
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Irish Sport Horse
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Cleveland Bay
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Württemberger
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Zangersheide
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Knabstrupper
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Orlov Trotter
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Camargue
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Icelandic Horse
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Pony of the Americas
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Quarter Pony
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Miniature Horse
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Clydesdale
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Shire
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Percheron
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Belgian Draft
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Suffolk Punch
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American Cream Draft
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Ardennes
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Breton
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Boulonnais
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Comtois
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Dutch Draft
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North Swedish Horse
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Norwegian Fjord
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Haflinger
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Gypsy Cob
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Irish Draught
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Welsh Pony and Cob
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Connemara Pony
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New Forest Pony
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Dartmoor Pony
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Exmoor Pony
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Shetland Pony
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Highland Pony
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Fell Pony
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Dales Pony
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Australian Pony
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Finnhorse
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Black Forest Horse
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