Dog fleas

Alternative names
Fleas; Siphonaptera

Fleas are wingless, blood-sucking insects that feeds on dog, cats, humans and other species.

Causes, incidence, and risk factors
Fleas prefer dog and cat hosts, but in the absence of a preferred host will use humans or other available animals as a host. Pet owners may not be bothered by fleas until their pet is away for an extended period of time and the fleas, in the absence of their normal host, begin to bite the owners. Bites frequently occur around the waist, ankles, armpits, and in the bend of the elbows and knees.


  • Rash with small bumps that itch and may bleed       o Located on the armpit or fold of a joint (at the elbow, knee, or ankle)       o The amount of skin affected increases over time (enlarging skin rash or lesion) or the rash spreads to other areas       o When pressed the area turns white (blanches to touch)  
  • Itching can be severe  
  • Itching can be generalized or restrictied to a skin rash  
  • Hives  
  • Swelling only around a lesion (sore) or injury  
  • Skin folds such as under the breasts or in the groin may be affected (intertrigo)

Note: Symptoms often begin suddenly (within hours).

Signs and tests
No testing is necessary.

The objective of treatment is to break the flea life cycle by treating the home, the pets, and the outside environment with insecticide. Home foggers and flea collars are not always effective. Birds and fish must be protected during spraying. If home treatments are ineffective, professional extermination may be needed.

Calamine lotion helps relieve itching.

Expectations (prognosis)
Once fleas are established, eliminating them requires persistence. The problem will continue until the fleas are eliminated.

Scratching can lead to a secondary skin infection.

Calling your health care provider
Apply home treatment and call your health care provider if there are signs of complications.

Prevention may not be possible in all cases. Use of insecticides may be helpful if fleas are common in your area. Professional extermination may be necessary in some cases.

Johns Hopkins patient information

Last revised: December 5, 2012
by David A. Scott, M.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.