Skin Disorders

~What to Do if Your Horse Has~
~A Skin Problem~
March 2002 Newsletter Information

The diagnosis of skin disease can be difficult. The picture is often clouded by the presence of wounds, insect bites, and secondary trauma caused by rubbing and biting at the skin. History becomes important in deciding what caused the initial insult. Considerations such as age, sex, breed, change in activity or diet, contact with other animals, emotional state, exposure to skin irritants, and environmental influences then become important determinants.
The following tables serve as an aid in the diagnosis of skin diseases. To facilitate identification, some skin ailments are listed in more than one table.

Does your horse show signs of...
If it does, refer to the suggested table below...

Table 1...tail rubbing, bites and scratches its skin, itchy skin disorder

Table 2...not causing excess discomfort, patchy hair loss on specific parts of the body, scabs and skinflakes, patches 1-2 inches in diameter with hair loss, scabs and skinflakes are often present

Table 3...painful skin disorder, infection on or beneath the skin, skin becomes abraded and infected as a result of rubbing and scratching, treatment of itchy skin disorder and secondary infected skin

Table 4...lumps, bumps, or growths beneath the skin

TABLE 1
Itchy Skin Disorders

Insect Bites

A common cause of itching in the fly season. Bumps, blisters, scabs, crusty areas,
and occasionally hair loss occur where insects bite.

Queensland Itch
(Culicoides Dermatitis)

The most common insect bite allergy in horses. Caused by gnats. Excretions,
crusts, and scabs. Intense itching with hair broken and rubbed off.

Ventral Midline Dermatitis

Caused by the migrating phase of a hair-like worm transmitted by gnats. Produces
moist crusty, shallow ulceration�s, typically centered along the midline on the
undersurface of the abdomen but sometimes on the face and eyelids. Hair is lost
around ulceration�s.

Hives

Round raised wheals scattered over the body with hair sticking out in patches.
Swelling of the face or eyelids can occur. Usually caused by inhaled allergens,
occasionally by allergens in the feed.

Irritant Contact Dermatitis

Red bumps with crusting and hair loss. Found around the muzzle, feet, legs,
saddle girth, and other areas in contact with irritants. Healed skin may turn white (depigmentation).

Allergic Contact Dermatitis

Same as above but requires repeated or continuous contact with allergen (e.g.,
horse tack, rubber bit). Dermatitis may spread beyond area of contact.

Pemphigus Foliaceus

A rare condition caused by an allergic response to a substance in the horses own
skin. Initially produces blisters, scabs, and scaly skin; later ulceration�s appear
with oozing of serum and crusting.

Mange

An intensely itchy skin disorder caused by mites. Red lumps followed by scabs,
crusts, and patches of hair loss are found all over the body, but especially on the
poll, mane, tail, and legs. Mites in ear canals cause head-shaking. Hair is lost
due to rubbing.

Chiggers

Intense itchy skin disorder caused by larva of mites. Traumatized skin found about
head, neck, chest, and legs. Seasonal and regional in chigger-infested
pastures.

Lice

Intense itching caused by 2 to 3 mm pale-colored insects found around head and
face, ears, topline, and base of tail. Hair is rubbed off; skin is excoriated.

Photosentivity Reaction

Requires exposure to sunlight. Redness, swelling, and weeping of serum. The
outer skin may peel as in sunburn. Usually confined to white or lightly pigmented
and hairless areas of the skin.

Summer Sores
(Habronema)

Caused by the larva of stomach worms deposited in open wounds and sores.
Occurs only in the fly season. Suspect this when a clean wound or sore suddenly
enlarges and becomes covered with a reddish-yellow tissue that bleeds easily.

Pinworms

Intense itching and tail rubbing primarily in weanling and young horses. "Ratty"
look to the tail.

TABLE 2
Disorders In Which Hair Is Lost

Patchy Shedding

Normal type of shedding. Produces bare patches up to 10 inches in diameter. Skin is healthy and hair grows back in 3 weeks.

Ringworm

Highly contagious skin fungus. Usually occurs in fall and winter. Commonly located in the saddle girth area. Scaly, crusty, or red circular patches with central hair loss are typical. May see matted clumps of hair, which fall out easily.

Seborrhea

A flaky, scaly, condition that looks like dandruff. Usually symmetrical. Bare circular patches occur where crusts peel off. May resemble ringworm.

Rain Scalds

A fungus infection that occurs in rainy weather. Characterized by tufts of matted hair, which look like large drops of water. Tufts come out leaving bare patches about 1 inch in diameter. May resemble ringworm. Skin often becomes secondarily infected.

Irritant Contact Dermatitis

Red bumps with crusting and hair loss. Found around the muzzle, feet, legs, saddle girth, and other areas in contact with irritants. Healed skin may turn white (depigmentation).

Allergic Contact Dermatitus

Same as above but requires repeated or continuous contact with allergen (e.g., horse tack, rubber bit). Dermatitis may spread beyond area of contact.

Tail Pyoderma

Furunculosis and abscess that occur on the skin of the tail from self-mutilation. The tail is severely abraded. Look for an underlying itchy skin problem such as tail mites or pinworms.

Selenium Toxicity

Loss of hair from mane and tail ("bob-tail" disease). Cracks in the hoof wall may cause severe lameness.

Lymphosarcoma

One or more subcutaneous masses or nodules� resembling hives, as seen in the cutaneous form.

TABLE 3
Skin Infections (Pyoderma)

Cellulitus and Abscess

Painful, hot inflamed skin or pockets of pus beneath the skin. Look for an underlying cause (itchy skin disorder, foreign body skin wound). One or more abscesses beneath the jaw suggests strangles.

Folliculitus
(Summer Rash)

Hair-pore infection that occurs in the saddle area in hot weather.

Furunculosis

A deep-seated hair-pore infection with draining sinus ttracts to the skin.

Tail Pyoderma

Furunculosis and abscesses that occur on the skin of the tail from self-mutilation. The tail is severely abraded. Look for an underlying itchy skin problem such as tail mites or pinworms.

Ulcerative Lymphangitis

Begins in extremity wounds with swelling of the leg and the appearance of abscesses along the lymphatic channels. The abscesses open and drain pus.

Malignant Edema

Begins in dirty wounds about the legs and face. A soft, hot, painful swelling that progresses rapidly and produces a toxic form of gas gangrene.

Poll-Evil

A deep-seated infection at the poll, characterized by swelling on one or both sides of the poll, then the formation of one or more draining sinus tracts to the skin.

Fistulous Withers

The same as poll-evil but occurs at the withers.

Rain Scalds

A fungus infection that occurs in rainy weather. Characterized by tufts of matted hair which look like large drops of water. Tufts come out leaving bare patches about 1 inch in diameter. May resemble ringworm. Skin often becomes secondarily infected.

Sporotrichosis

A draining sore or ulcer at the site of a puncture wound, usually on the leg. Nodules appear along the lymphatic channels, ulcerate, discharge pus, and heal slowly. Caused by a fungus.

Grease Heel
(Mud Fever)

An infection at the back of the fetlocks and/or the heels, characterized by a greasy exudate that mats the hair. Proceeds to ocellulitus and ulceration. Grape-like clusters may appear.

Summer Sores
(Habronema)

Caused by the larva of stomach worms deposited in open wounds and sores. Occurs only in the fly season. Suspect this when a clean wound or sore suddenly enlarges and becomes covered with a reddish-yellow tissue that bleeds easily.

Ventral Midline Dermatitis

Caused by the migrating phase of a hair-like worm transmitted by gnats. Produces moist crusty, shallow ulcerations, typically centered along the midline on the undersurface of the abdomen but sometimes on the face and eyelids. Hair is lost around ulceration�s

TABLE 4
Lumps, Bumps, and Growths on or Beneath the Skin

Warts
(Papillomas)

Smooth, raised, flesh-colored bumps on the muzzle and lips of young horses. Usually disappear in 3 months.

Sarcoid

The most common tumor in horses. Takes a variety of shapes. May be flat with hair loss, ulcerated, or cauliflower. Found around eyes and anywhere on the body. Affects horses of all ages.

Tender Knots

Frequently found at the site of a shot or vaccination. Resolve spontaneously. Often painful.

Cattle Grubs

Painful nodules beneath the skin; found at the withers, neck, and back. May have a breathing hole to the skin.

Squamous Cell Carcinoma

A hard, flat or ulcerating growth found on older horses of the lightly pigmented breeds, especially in hairless areas exposed to sunlight. Most common on the face and genitalia. Does not heal.

Melanoma

A dark brown to black nodular growth, usually on the underside of the tail; sometimes about the vulva, anus, male genitalia, eyes, or mouth. Commonly found on old grey horses.

Phycomycosis
(Leeches)

A deep-seated fungus infection that often occurs at the site of a cut, usually on the leg but sometimes on the head and abdomen. A fast-growing bulbous mass of greyish-pink tissue that discharges infected material through numerous sinus tracts.

Lymphosarcoma

One or more subcutaneous masses or nodules� resembling hives, as seen in the cutaneous form.

***Reference material used for this page can be found in the "Horse Owners Veterinary Handbook" second edition.

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Insect Bites	A common cause of itching in the fly season. Bumps, blisters, scabs, crusty areas, and occasionally hair loss occur where insects bite.
Queensland Itch (Culicoides Dermatitis)	The most common insect bite allergy in horses. Caused by gnats. Excretions, crusts, and scabs. Intense itching with hair broken and rubbed off.
Ventral Midline Dermatitis	Caused by the migrating phase of a hair-like worm transmitted by gnats. Produces moist crusty, shallow ulceration�s, typically centered along the midline on the undersurface of the abdomen but sometimes on the face and eyelids. Hair is lost around ulceration�s.
Hives	Round raised wheals scattered over the body with hair sticking out in patches. Swelling of the face or eyelids can occur. Usually caused by inhaled allergens, occasionally by allergens in the feed.
Irritant Contact Dermatitis	Red bumps with crusting and hair loss. Found around the muzzle, feet, legs, saddle girth, and other areas in contact with irritants. Healed skin may turn white (depigmentation).
Allergic Contact Dermatitis	Same as above but requires repeated or continuous contact with allergen (e.g., horse tack, rubber bit). Dermatitis may spread beyond area of contact.
Pemphigus Foliaceus	A rare condition caused by an allergic response to a substance in the horses own skin. Initially produces blisters, scabs, and scaly skin; later ulceration�s appear with oozing of serum and crusting.
Mange	An intensely itchy skin disorder caused by mites. Red lumps followed by scabs, crusts, and patches of hair loss are found all over the body, but especially on the poll, mane, tail, and legs. Mites in ear canals cause head-shaking. Hair is lost due to rubbing.
Chiggers	Intense itchy skin disorder caused by larva of mites. Traumatized skin found about head, neck, chest, and legs. Seasonal and regional in chigger-infested pastures.
Lice	Intense itching caused by 2 to 3 mm pale-colored insects found around head and face, ears, topline, and base of tail. Hair is rubbed off; skin is excoriated.
Photosentivity Reaction	Requires exposure to sunlight. Redness, swelling, and weeping of serum. The outer skin may peel as in sunburn. Usually confined to white or lightly pigmented and hairless areas of the skin.
Summer Sores (Habronema)	Caused by the larva of stomach worms deposited in open wounds and sores. Occurs only in the fly season. Suspect this when a clean wound or sore suddenly enlarges and becomes covered with a reddish-yellow tissue that bleeds easily.
Pinworms	Intense itching and tail rubbing primarily in weanling and young horses. "Ratty" look to the tail.

Patchy Shedding	Normal type of shedding. Produces bare patches up to 10 inches in diameter. Skin is healthy and hair grows back in 3 weeks.
Ringworm	Highly contagious skin fungus. Usually occurs in fall and winter. Commonly located in the saddle girth area. Scaly, crusty, or red circular patches with central hair loss are typical. May see matted clumps of hair, which fall out easily.
Seborrhea	A flaky, scaly, condition that looks like dandruff. Usually symmetrical. Bare circular patches occur where crusts peel off. May resemble ringworm.
Rain Scalds	A fungus infection that occurs in rainy weather. Characterized by tufts of matted hair, which look like large drops of water. Tufts come out leaving bare patches about 1 inch in diameter. May resemble ringworm. Skin often becomes secondarily infected.
Irritant Contact Dermatitis	Red bumps with crusting and hair loss. Found around the muzzle, feet, legs, saddle girth, and other areas in contact with irritants. Healed skin may turn white (depigmentation).
Allergic Contact Dermatitus	Same as above but requires repeated or continuous contact with allergen (e.g., horse tack, rubber bit). Dermatitis may spread beyond area of contact.
Tail Pyoderma	Furunculosis and abscess that occur on the skin of the tail from self-mutilation. The tail is severely abraded. Look for an underlying itchy skin problem such as tail mites or pinworms.
Selenium Toxicity	Loss of hair from mane and tail ("bob-tail" disease). Cracks in the hoof wall may cause severe lameness.
Lymphosarcoma	One or more subcutaneous masses or nodules� resembling hives, as seen in the cutaneous form.

Cellulitus and Abscess	Painful, hot inflamed skin or pockets of pus beneath the skin. Look for an underlying cause (itchy skin disorder, foreign body skin wound). One or more abscesses beneath the jaw suggests strangles.
Folliculitus (Summer Rash)	Hair-pore infection that occurs in the saddle area in hot weather.
Furunculosis	A deep-seated hair-pore infection with draining sinus ttracts to the skin.
Tail Pyoderma	Furunculosis and abscesses that occur on the skin of the tail from self-mutilation. The tail is severely abraded. Look for an underlying itchy skin problem such as tail mites or pinworms.
Ulcerative Lymphangitis	Begins in extremity wounds with swelling of the leg and the appearance of abscesses along the lymphatic channels. The abscesses open and drain pus.
Malignant Edema	Begins in dirty wounds about the legs and face. A soft, hot, painful swelling that progresses rapidly and produces a toxic form of gas gangrene.
Poll-Evil	A deep-seated infection at the poll, characterized by swelling on one or both sides of the poll, then the formation of one or more draining sinus tracts to the skin.
Fistulous Withers	The same as poll-evil but occurs at the withers.
Rain Scalds	A fungus infection that occurs in rainy weather. Characterized by tufts of matted hair which look like large drops of water. Tufts come out leaving bare patches about 1 inch in diameter. May resemble ringworm. Skin often becomes secondarily infected.
Sporotrichosis	A draining sore or ulcer at the site of a puncture wound, usually on the leg. Nodules appear along the lymphatic channels, ulcerate, discharge pus, and heal slowly. Caused by a fungus.
Grease Heel (Mud Fever)	An infection at the back of the fetlocks and/or the heels, characterized by a greasy exudate that mats the hair. Proceeds to ocellulitus and ulceration. Grape-like clusters may appear.
Summer Sores (Habronema)	Caused by the larva of stomach worms deposited in open wounds and sores. Occurs only in the fly season. Suspect this when a clean wound or sore suddenly enlarges and becomes covered with a reddish-yellow tissue that bleeds easily.
Ventral Midline Dermatitis	Caused by the migrating phase of a hair-like worm transmitted by gnats. Produces moist crusty, shallow ulcerations, typically centered along the midline on the undersurface of the abdomen but sometimes on the face and eyelids. Hair is lost around ulceration�s

Warts (Papillomas)	Smooth, raised, flesh-colored bumps on the muzzle and lips of young horses. Usually disappear in 3 months.
Sarcoid	The most common tumor in horses. Takes a variety of shapes. May be flat with hair loss, ulcerated, or cauliflower. Found around eyes and anywhere on the body. Affects horses of all ages.
Tender Knots	Frequently found at the site of a shot or vaccination. Resolve spontaneously. Often painful.
Cattle Grubs	Painful nodules beneath the skin; found at the withers, neck, and back. May have a breathing hole to the skin.
Squamous Cell Carcinoma	A hard, flat or ulcerating growth found on older horses of the lightly pigmented breeds, especially in hairless areas exposed to sunlight. Most common on the face and genitalia. Does not heal.
Melanoma	A dark brown to black nodular growth, usually on the underside of the tail; sometimes about the vulva, anus, male genitalia, eyes, or mouth. Commonly found on old grey horses.
Phycomycosis (Leeches)	A deep-seated fungus infection that often occurs at the site of a cut, usually on the leg but sometimes on the head and abdomen. A fast-growing bulbous mass of greyish-pink tissue that discharges infected material through numerous sinus tracts.
Lymphosarcoma	One or more subcutaneous masses or nodules� resembling hives, as seen in the cutaneous form.