Understanding Rain Rot: Causes, Symptoms, Prevention, and Treatment

Rain rot leads to scabs that cause the hair to fall out in clumps

Rain rot—also commonly known as mud fever, rain scald, or scratches—is a skin condition that affects horses and other livestock. Despite its misleading name, rain rot is not caused by rain itself, but by a bacterium known as Dermatophilus congolensis. This opportunistic pathogen thrives in wet, humid conditions and can cause significant skin irritation and damage if left unchecked.

What is Rain Rot?

Rain rot refers to a bacterial skin infection caused by Dermatophilus congolensis, a microorganism found in soil and sometimes present on the skin of animals and even humans in a dormant state. Under favorable conditions—namely warmth and persistent moisture—the bacterium becomes active and leads to an inflammatory infection of the skin.

This condition is especially prevalent in livestock such as horses, cattle, and goats. While not typically life-threatening, it can be painful, unsightly, and, in severe cases, result in more extensive skin damage.

How Rain Rot Develops

The infection typically begins when the horse's skin becomes compromised. Microtears caused by insect bites, friction, or allergic reactions create a gateway for the bacteria. The presence of constant moisture—from rain, sweat, or muddy conditions—allows the bacteria to multiply rapidly. This leads to the formation of characteristic lesions: crusty scabs that trap tufts of hair, resembling small paintbrushes when removed.

When these scabs fall away or are picked off, they leave behind bald patches of skin, which may continue to expand if the infection spreads or remains untreated. In chronic or severe cases, the bacteria can invade deeper skin layers, resulting in more extensive and painful damage.

Risk Factors

Although any horse can develop rain rot, certain conditions increase susceptibility:

• Compromised Skin Integrity: Horses with insect bite reactions, allergic dermatitis, or existing wounds are more vulnerable.

• Weakened Immune System: Older horses, those with chronic illness, or those experiencing stress are more likely to suffer from rain rot.

• Environmental Conditions: Wet, muddy fields, high humidity, and poor sheltering increase the risk of infection.

• Heavy Coats and Feathering: Breeds with dense coats or feathered legs (such as draft horses) are at higher risk, as moisture tends to get trapped more easily.

  
  

If you suspect your horse has rain rot, it’s helpful to review their overall health by checking their vital signs, including temperature and heart rate.

Common Areas Affected

The condition is most commonly found along the horse’s topline—particularly the back, withers, and croup—where rainwater tends to collect and linger. However, it may also appear on the:

• Face

  

  Rain rot can appear anywhere on the face. The facial crest and upper cheek are commonly affected areas.

• Trunk

  

  This is the most common presentation of rain rot

• Legs, especially the pasterns

  

  Example of rain rot affecting the pastern: this is commonly called "mud fever"

In cases where the infection manifests around the pasterns and fetlocks, it is often referred to specifically as scratches or mud fever. This variation can be particularly painful due to the movement of skin in these areas and, if untreated, can cause enough discomfort to result in lameness.

Symptoms to Watch For

• Tufts of hair that pull out easily with attached scabs

• Raw, bald spots beneath scabs

• Warm, inflamed, or sensitive skin

• Thickened or crusted skin over time

• Painful lesions, especially on the lower limbs

Notably, unlike other equine skin conditions such as sweet itch, rain rot typically does not cause significant itching, though the lesions themselves may be tender to the touch.

Learn more on How to Tell If Your Horse Is Sick: Early Signs Every Owner Should Know

Prevention Strategies

Preventing rain rot involves minimizing the conditions that allow D. congolensis to thrive:

• Daily Grooming: Regular brushing helps to remove dirt, sweat, and potential bacterial contamination from the skin.

• Timely Bathing: Periodic bathing with an anti-microbial shampoo can help reduce bacterial populations on the skin.

• Dry Environment: Ensure horses have access to shelter during prolonged wet weather. Avoid turnout in excessively muddy paddocks when possible.

• Prompt Cleaning: Remove caked mud from legs and belly after turnout. Do not allow damp hair and dirt to accumulate.

• Feathered Breeds: Take extra precautions with horses that have long hair on the legs, such as clipping and drying the feathers.

  
  

Containment and Hygiene

Rain rot can be contagious through shared tack, brushes, or close contact. To prevent spreading it among horses:

• Isolate Affected Horses: Keep infected animals separate during treatment.

• Disinfect Equipment: Clean grooming tools, blankets, saddle pads, and even stalls thoroughly after contact.

• Wash Hands and Change Clothes: This is especially important if handling multiple horses, to avoid transmitting the bacteria manually.

While rain rot itself doesn’t cause lameness, severe skin discomfort can lead to movement issues. Learn how to assess your horse properly with our comprehensive lameness guide.

Treatment and Veterinary Intervention

Mild cases of rain rot can often be managed at home with thorough hygiene and over-the-counter anti-bacterial or anti-fungal topical treatments. However, in more advanced cases, veterinary intervention may be necessary. A vet may prescribe:

• Systemic Antibiotics: If lesions are widespread or recurrent.

• Topical Antimicrobials: Medicated ointments, sprays, or shampoos to eliminate bacteria from the skin surface.

• Anti-inflammatory Medication: To reduce pain and swelling, especially if lesions are interfering with movement.

Horses should be kept dry throughout the treatment process, and scabs should not be forcibly removed if they are not ready to slough off, as this can cause further skin damage and delay healing.

Some owners also explore immune and circulation support products—like capillary strength powders—as part of their horse’s recovery routine

Conclusion

Rain rot is a common but preventable skin condition in horses, triggered by a combination of environmental factors and bacterial invasion. Understanding its causes, recognizing the early signs, and maintaining strict grooming and hygiene protocols are key to keeping your horse healthy and comfortable. While most cases are easily managed with good stable practices, severe or persistent infections should always be evaluated by a veterinarian.

By staying proactive, horse owners can minimize the risk of rain rot, ensuring their animals remain in optimal skin health year-round.

RAIN ROT Q&A

What is rain rot in horses?

Rain rot (also known as rain scald, mud fever, or scratches) is a bacterial skin infection in horses caused by Dermatophilus congolensis. It typically affects areas where moisture accumulates, such as the back, legs, and face, causing scabs, hair loss, and skin irritation.

What causes rain rot in horses?

Rain rot is caused by the bacterium Dermatophilus congolensis, which lives in the soil and on the skin in a dormant state. It becomes active under wet, humid conditions, especially when a horse’s skin is compromised by insect bites, friction, or allergies.

Is rain rot contagious between horses?

Yes, rain rot can be contagious, especially through shared grooming tools, tack, or close contact. It's important to isolate infected horses and disinfect equipment to prevent the spread of the bacteria to other animals.

What does rain rot look like on a horse?

Rain rot typically appears as:

• Tufts of matted hair that pull out easily

• Crusty scabs

• Raw bald spots underneath the scabs

• In advanced cases, painful sores, especially on the legs (commonly called scratches)

  
  

What areas of the horse are most affected by rain rot?

Rain rot most commonly affects the topline (back, withers, croup), but can also appear on the:

• Face

• Neck and shoulders

• Legs and pasterns

• Belly and flanks

Breeds with thick coats or feathered legs (e.g., draft horses) are particularly susceptible.

Does rain rot make horses itchy?

Unlike fungal conditions, rain rot usually does not cause itching. However, it can become painful, especially in areas with movement like the backs of the pasterns, where it may lead to lameness if untreated.

How do you treat rain rot on a horse?

Treatment includes:

• Keeping the horse dry

• Gently removing scabs once they loosen

• Bathing with antimicrobial shampoos (chlorhexidine or iodine-based)

• Disinfecting grooming tools and tack

• Veterinary intervention for severe or spreading infections (antibiotics may be prescribed)

  
  

How long does rain rot take to heal?

With proper care, mild cases of rain rot may heal within 7–14 days. Severe cases involving large areas or deep infections may take several weeks and require medical treatment.

Can you prevent rain rot in horses?

Yes, rain rot prevention is possible with good stable and grooming practices:

• Regular grooming and bathing

• Keeping horses dry and sheltered during wet weather

• Removing mud from coats and legs promptly

• Using antimicrobial products during high-risk seasons

• Clipping or drying feathered legs regularly

  
  

Is rain rot the same as scratches or mud fever?

They are related but can refer to different presentations:

• Rain rot often affects the topline and body.

• Scratches or mud fever refers to the same infection when it affects the lower limbs, especially around the pasterns, and can cause lameness.

  
  

Can humans get rain rot from horses?

Dermatophilus congolensis can rarely infect humans, particularly those with weakened immune systems or broken skin. However, it is not commonly transmitted to humans. Wearing gloves and practicing hygiene after grooming is advised.

When should I call the vet for rain rot?

Contact a veterinarian if:

• The infection spreads rapidly

• Lesions become painful or swollen

• The horse shows signs of lameness

• There is no improvement within a week of treatment

Veterinary diagnosis can confirm the infection and ensure appropriate antibiotics or anti-inflammatory medications are prescribed.

RAIN ROT SELF ASSESSMENT QUIZ

Part 1: Multiple Choice Questions

1. What is the primary cause of rain rot in horses?

A. Fungus from hay

B. Virus in standing water

C. Dermatophilus congolensis bacteria

D. Mites in muddy soil

2. Which of the following factors increases a horse’s risk of developing rain rot?

A. Dry, arid climate

B. Grooming twice a day

C. Thick feathering on the pasterns

D. Frequent exposure to sand arenas

3. What is the term for rain rot that occurs on the back of a horse’s pasterns or lower limbs?

A. Sweet itch

B. Rain scald

C. Mud fever or scratches

D. Thrush

4. Which symptom is most commonly associated with rain rot?

A. Severe itching

B. Loss of hair in clumped scabs

C. Blistering hooves

D. Nasal discharge

5. How can Dermatophilus congolensis be spread between horses?

A. Through airborne spores

B. Through contaminated grooming tools

C. Through contaminated feed

D. It cannot be transmitted

Part 2: True or False

6. ___ Rain rot can become active during hot and humid conditions.

7. ___ Horses with healthy skin and strong immune systems are completely immune to rain rot.

8. ___ Rain rot is always itchy and causes extreme discomfort.

9. ___ Grooming equipment should be disinfected after use on an infected horse.

0. ___ Rain rot may reoccur under favorable conditions even after healing.

Part 3: Short Answer Questions

11. What is the most common body area affected by rain rot in horses?

12. Why is it important to avoid removing rain rot scabs before they loosen naturally?

13. List at least two ways to prevent rain rot from developing on your horse.

14. What should you do if your horse develops widespread or painful rain rot that does not improve within a week?

15. How can moisture and mud contribute to the development of rain rot?

Answer Key

Part 1: Multiple Choice

1. C – Dermatophilus congolensis bacteria

2. C – Thick feathering on the pasterns

3. C – Mud fever or scratches

4. B – Loss of hair in clumped scabs

5. B – Through contaminated grooming tools

   
   

Part 2: True or False

6. True

7. False – They are less likely, but not immune

8. False – Rain rot is not usually itchy

9. True

10. True

    
    

Part 3: Short Answer (Sample Responses)

11. The horse’s topline (back, withers, and croup) is the most common area affected.

12. Forcibly removing scabs can damage healthy tissue underneath and worsen the infection, possibly leading to deeper skin trauma.

13.

• Regular grooming and bathing with antimicrobial shampoos

• Keeping the horse dry and out of prolonged wet conditions

• Providing shelter during rain

• Cleaning mud off promptly

14. Contact a veterinarian for appropriate treatment, which may include antibiotics or anti-inflammatory medications.

15. Moisture softens the skin and creates an environment where bacteria can thrive, especially if the skin is broken or compromised, allowing infection to take hold.