What is a common clinical sign of flea allergy dermatitis?

Intense itching and inflammation of the skin is a hallmark of flea allergy dermatitis (FAD). This condition arises when an animal develops a hypersensitivity reaction to the saliva of fleas. When fleas bite, they inject saliva that contains allergens into the skin, triggering an immune response. This leads to significant itching, which drives pets to scratch, bite, or lick the affected areas, resulting in inflammation and hair loss. The intense scratching can often lead to secondary infections due to skin trauma.

In comparison to the other options, hair loss on the tail may occur as a result of excessive scratching in affected areas but is not a defining feature specific to flea allergy dermatitis. Dry skin with no inflammation doesn't align with the typical clinical presentation of FAD, since the reaction typically involves inflammation. Redness around the eyes could indicate other issues such as allergies or irritations but is not directly associated with flea allergy dermatitis. Thus, the intense itching and inflammation of the skin captures the essence of the primary clinical sign associated with this condition.