Rain rot

Veterinary advice should be sought before applying any treatment or vaccine.

Rain Rot

Rain Scald, Dermatophilosis, Mud Fever

Dermatophilosis (rain rot) is one of the most common skin infections of horses, resulting in pustular crusting and matting of the hair coat. It is caused by Dermatophilus congolensis, which is an actinomycete, a fungi-like bacteria which is predominately found in soil. The organism is especially attracted to warm, damp conditions. It is most often seen in horses living in areas with a wet, mild climate or in dry regions which develop a large amount of seasonal moisture.

D. congolensis is able to infect multiple animal species, many can act as reservoirs. It is maintained in environments by living within chronic skin lesions of carrier animals, which become reactivated with excessive exposure to moisture. In order to infect horses, there needs to be a break down of the skin defensive barrier, such as that caused by:
  • Biting insects and arthropods
  • Excessive wetting: Continuous morning dew exposure, frequent bathing or wet conditions
  • Physical trauma: Caused by penetrating thorns or awns, abrasions, lesions or wounds
  • Friction: Excessive rubbing of skin against objects
  • Self-mutilation
What it looks like
Papules initially develop, which turn into pustules. The hairs become matted together and form thick crusts, which can easily be removed in clumps. The underlying skin is reddened, scabby, with mild erosions or evidence of proliferation and exudate.


Matted haircoat, which comes out in clumps


  • History
  • Clinical signs
  • Physical exam
  • Bacterial culture
  • Skin biopsy



Daily cleansing of lesionsCleanse affected area using topical disinfectants, gently try to remove crusts.
Repeat for 7 to 10 days.
It may be beneficial to locally clip the affected area on the horse
Environmental managementProvide protection from wet environments (keep out of pasture fields with morning dew, bring in stall during rain storms, thoroughly dry following baths).
Disinfect all grooming brushes and any materials that potentially came into contact with the organism.
AntibioticsMay be indicated if horses are severely affected.


  • Minimizing exposure to excessive moisture
  • Periodically bathing with topical antibacterial shampoos, making sure to fully dry off haircoat
  • Insect repellents

Scientific Research

General Overviews

  • rainrot icon
  • rainrot icon

Risk Factors

  • Horses with thick coats
  • Living in hot and humid environments, such as South Florida
  • Prior skin trauma
  • Poorly ventilated, infrequently cleaned, damp stalls