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Why Is My Horse Losing Hair? Big Patches Are Coming Off!

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Recently my granddaughter’s horse began losing hair, especially during grooming when it comes off in big patches. We decided to talk to the vet and do some research to find out why her horse was losing hair.

Horses lose hair because of insects, bacteria, skin infections, heat, medical conditions, or allergies. Horses also itch and rub irritated areas creating bald spots. Hair loss can be permanent or temporary and can affect specific areas or include the entire body.

Most horse owners want their horse’s coats to look shiny and healthy, and hair loss has the opposite effect. But more importantly, hair loss may be an early sign of an underlying medical condition. Many of the causes of equine hair loss can be prevented and treated with over-the-counter products.

Picture of a horse with rain rot.

Common causes of hair loss in horses.

Many things cause hair loss in horses, but I’m going to focus on the most common reasons, parasites, bacterial infections, and some medical conditions. To find what is causing the animal to shed, it’s critical to determine if the origin is internal or external.

In other words, the cause is likely insects attacking your horse or a medical condition. Insects destroy a horse’s coat, cause bleeding and sores, and irritate the animal to the point that it rubs itself bald to get relief.

Typically horses that rub their hair off also leave broken strands, and the underlying area is irritated and red. I recently bought five young horses, and all had varying stages of hair loss.

Insects cause horses to lose hair.

Bloodsucking insects wreak havoc on horses. They are a physical and emotional nuisance that can cause their host to become nervous and underperform.

These arthropods are often the reason you see horses stomping, rubbing, and continuously switching their tails. Insects not only increase an animal’s stress level; they negatively affect their health and transmit diseases.

Some insects are large enough to be easily visible, but some are so small you never see them. An arthropod can be as tiny as 1 millimeter, which is a problem because they can infest your horse, and you may never know they are there until you find crusty skin or hair loss.

Picture of a horse with horseflies around its face,

Horse Flies

Female horse flies are the biters; they sink their cutters into a horse and suck their blood. But the real problem is that the blood continues to flow after they fly off.

The blood released by horse flies attracts other pests that congregate in the affected area.

Gnats or midges

Biting gnats are tiny but pack a painful bite. These creatures swarm around your horse’s belly and are constantly swished off with their tails.

Their painful bite opens the flesh so they can suck blood from their host. The sheer numbers in the swarm can create large blood patches that turn into scabs and cause animals to lose hair.

Their bites not only cause sores, but they are incredibly itchy, so horses rub their body against poles and trees to get relief. The consequence of this action is scraping the area bald. Horses often become allergic and have severe reactions to gnat bites.

These flying and biting gnats also are carriers of Onchocerca cervicalis, a threadlike parasitic worm causing skin lesions and itching in horses. They are so small that a skin scrape is typically necessary to confirm a diagnosis. Ivermectin is effective in preventing Onchoceraca cervicalis.

Besides liking the under the belly of horses, they also fleed around their manes and tails. If there are bright spots to these annoying insects, it’s that they only fly in the warm months and are active primarily around dusk.

They also are weak fliers and can be kept off your horses with a fan. Gnats are typically picked up in fields, so in addition to topical spray, spraying pastures with insecticides can reduce their populations.

Stable Flies

Stable flies are sometimes called the “biting flies” because of their painful bite, and they don’t discriminate; they bite just about any mammal. They are bloodsuckers and are typically most active in the spring.

Stable flies look similar to a common housefly, they are about 1/4 inch long, but unlike a housefly, they have a long snout they use to suck blood from a host.

They deposit disease and infect open wounds with worm larvae, which creates infection and inflammation. The sores these pests make lead to itching and hair loss.

Horn fly

Horn flies are small flies that cluster around cattle. They got their name because they were often observed around cows’ horns, but they are most often seen on the backs of cattle or under their bellies.

They are bloodsuckers and do attack horses kept in pastures with cattle. These pests travel in swarms of thousands, and when horses are attacked, they experience extreme itchiness and hair loss, typically on the side of the neck or under their belly.

Black Flies

Black flies are small biting flies; they are also called buffalo gnats. They fly in swarms, but unlike the other biting flies, they are not known for spreading disease.

However, their bite does cause swelling, bleeding, and itching. The bleeding and itching lead to hair loss. And because they congregate in such large numbers, they are incredibly annoying.

Black flies typically feed on the horse’s head, neck, and stomach region.


Mosquitos are prevalent in my area of south Louisiana and are causes of skin irritations, sores, and hair loss. They also transmit infectious diseases, and of course, their bites are incredibly itchy, and horses repeatedly rub the affected areas.


Botflies cause most of the problems in the stomach and intestines of horses. But they also cause lesions that provide a location for infections and hair loss.

Botflies lay eggs on horses’ front legs, shoulders, and lips. These eggs make their way into a horse’s mouth and travel to the stomach. The larvae primarily pass through the horse in its manure.

However, some migrate under the skin in mucous membranes and erupt. Botflies don’t bite and are primarily an intestinal problem for horses.


There are a couple of species of biting horse lice. These pests feed on blood and are typically found on a horse’s head, neck, mane, and tail. Lice bite and annoy horses, causing them to bite themselves, stomp, and rub.

Lice don’t directly cause a horse to lose hair, but their irritation makes animals continuously rub against fence posts and trees until their hair comes off.


Ticks are becoming more prevalent on horses. They can cause skin irritation, resulting in the animal rubbing on posts or trees and creating hair loss.

It’s essential to check your horse for ticks during your daily grooming. They transmit some severe diseases, such as Lyme disease, and cause anemia due to blood loss.

Ticks live in grass and board horses’ legs when they walk bye. They typically migrate to horses’ chests, underbelly, or inside their flank.

Bacterial infections

  • Rain Rot

Rain rot is a bacterial infection that affects horses’ toplines and can cause horses to lose big patches of hair. The bacteria is picked up in various ways and typically attacks weakened skin regions.

Horse skin becomes vulnerable because of excessive moisture or through insect bites. Horses with diminished immune systems are the most likely ones to be affected.

Rain rot causes raised hair with lesions that form bumps and crust. When the crust is rubbed off, patches of hair are removed as well. The primary areas affected are the head, back, and hindquarters of horses.

If rain-rot is left untreated, it can spread rapidly.

  • Ringworm

Ringworm is not primarily a bacterial infection, but I included it here because broken skin caused by ringworms often leads to secondary bacterial infections.

Ringworm is a skin infection caused by a fungus that infects horses and other animal species, including humans. Ringworm skin lesions start as small raised spots with hair loss.

It is a dermatophyte infection and easily transmittable between horses, especially those that share tack or stalls. The fungus is durable and can survive for long periods on items and barn structures.

These lesions multiply and form more extensive thick dry scabs. The lesions are typically sore and itchy. If left untreated, the condition often becomes extensive.

The fungus is difficult to control because a horse can be infected for weeks without showing signs of infection. And because it has no symptoms, it’s allowed to be around and expose other animals to the disease.

Ringworm isn’t easy to diagnose, so I suggest you consult a vet; they can pluck a hair or two and test it for the fungus that causes ringworm. Most cases of ringworm can be treated with antifungal cream and medicated shampoo.

Picture of two horse in a paddock one with hair loss,

Medical conditions cause horses to lose hair.

Pastern Dermatitis

Pastern dermatitis is most prevalent in horse breeds with feathers on their lower legs, like those on Friesians and Clydesdales. The thick hair traps moisture and bacteria which causes irritation to the skin of the lower legs, (underneath the feathers).

Your horses don’t have to have feathers to develop pastern dermatitis. Horses kept in pastures, paddocks, or stalls where their lower legs stay wet are also likely to create pastern dermatitis. If the ground is unsanitary, the risk is increased further.

It displays as redness, crusting, and hair loss in the pattern region. Its caused by various reasons, including bacteria, fungus, and mites. The easiest way to prevent the condition is to keep the area dry; I recommend blow-drying the long hair surrounding your horse’s lower legs after washing.

Picture of a Friesian horse with long feathers, they are susceptible to pattern dermatitis and hair loss.

Skin Cancer

A sarcoid is a benign cancerous skin tumor that can cause hair loss. They typically present around the animal’s head and groin and in wounds. They can be mistaken for proud flesh.

There are different types of sarcoid tumors. Verrucose are flat and resemble ringworm syndrome or scars; this is the least aggressive type of sarcoid. Other types are very aggressive, such as fibroblastic, and need attention quickly.

Skin cancer tumors are not painful and are caused by bovine papilloma or BPV. Its believed, but not proven, that the disease is transmittable from horse to horse. An interesting fact is that papillon is the same virus linked to cervical cancer in women.

Cancer tumors can be treated with vaccines, surgery, laser, or cryotherapy. Contact your vet if you suspect your horse has skin cancer. He will recommend the best path forward.

 Seasonal Alopecia

Like most other animals, horses shed and grow protective hair coats as the seasons change. For horses, their coat thickens in winter and begins to thin in the spring.

However, some horses lose this natural balance and lose and grow hair outside of the regular schedule. This condition is called seasonal alopecia and is likely caused by a hormonal imbalance.

Horses with seasonal alopecia lose hair but typically grow it back without any adverse side effects. Just remember to keep your horse warm in the winter if it fails to develop a thick coat.

Particular grass or hay can cause hair loss.

The trace mineral selenium can cause hair loss, brittle hooves, and signs of lameness. It is an essential mineral in small doses but has severe consequences when too much is eaten.

An acute overdose of selenium can kill a horse. But selenium toxicity is typically a chronic condition. Some hay and grass grown in soil with high selenium levels and eaten regularly by a horse can lead to chronic selenium toxicity and hair loss.


What promotes hair growth in horses?

Healthy hair growth in horses is promoted by a balanced diet rich in protein, vitamins, and minerals, regular exercise, good grooming practices, and avoiding stress. Additionally, providing the horse with a clean and comfortable environment and addressing any underlying medical conditions promotes healthy hair growth

Can you ride a horse if it’s lost patches of hair?

Deciding to ride your horse or not because it has hair loss depends on the patch’s location and its cause. If the area looks infected, moist, or raw, don’t ride the horse. For some horses with a mild case of hair loss that is dry, you could ride for brief periods and then bathe the horse afterward.

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