What is the etiology of dermatitis caused by flea bites?

The dermatitis is caused by the irritant molecules and numerous allergens that make up the flea's saliva.
A protein called Ctef1 is responsible for 90% of the IgE production in DAPP in the canine species.
The flea injects its saliva into the dermis, causing the degranulation of mast cells and a potent inflammatory reaction.