Inflammatory mediators like histamine cause cutaneous nerve stimulation which leads to pruritus sensation and scratch.Affected areas show erythema ( redness ) or rashes.In chronic patients alopecia and darkness of the skin can be seen.
Most often pruritus in dogs is caused by :
1-Ectoparasites: flea, lice,,scabies, insect biting,demodicosis
2- Infection agents: Staphylococcal pyoderma , Malassezia dermatitis
3-Allergies: contact,food and atopic dermatitis
On the basis of examination, distribution of lesions,flea comb,skin scraping or cytology test,therapeutic trial, skin allergy test,rarely skin biopsy diagnosis is done.
It is done on the basis of diagnosis such as anti-flea spray for flea infestation.