Flea Allergy Dermatitis (FAD)

FAD is the most common skin disease found in dogs and cats caused by an external parasite. A flea will bite the pet to take a blood meal, and the saliva of the flea will cause an allergic chemical reaction of the skin. Adult fleas are the only cause of this disease as they require blood to survive. Other pupae and larval stages of the flea may be found on your pet and in the environment but won’t be the cause of skin irritation.


  • Red sore skin
  • Scabbing of the skin especially on the hind end near the base of the tail where the pet can reach and chew the skin open
  • Hair loss
  • Severe itching
  • Hypersensitivity when touching the skin in affected areas
  • Flea dirt visible when using a fine comb, flea feces (digested blood) looks like small flecks of pepper and when on a white damp cloth can turn red


  • A quick kill flea treatment usually oral tablets are preferred as the skin is usually too sore and scabby to use topical treatments
  • Flea treatments for at least 3-4 months to ensure all life stages on the pet and in the house are killed
  • Flea spray if needed in the environment
  • Often if there is a severe enough allergy a steroid injection will be given to help soothe and reduce the itching
  • Oral antibiotics may also be prescribed if an open sore is infected


  • Flea prevention is recommended as soon as the temperature starts to rise until the first snowfall stays on the ground
  • Even if the pet doesn’t go outside, there is still a risk of picking up a ‘hitchhiker’ flea and bringing it into your house

Written by: Carly Jeffery, Practice Manager