Herpes Zoster (Shingles): This is the most likely diagnosis due to the characteristic distribution of vesicles along a dermatomal pattern, which the helix of the ear follows. The Ramsay Hunt syndrome, a complication of shingles, can also involve the ear.

Contact Dermatitis: Allergic or irritant contact dermatitis can cause vesicles on the ear, especially if the patient has been exposed to new earrings, hair products, or other potential allergens or irritants.
Impetigo: A contagious bacterial infection that can cause vesicles or pustules on the skin, including the ear.
Eczema (Atopic Dermatitis): Can cause vesicular lesions, especially in individuals with a history of atopic diseases.

Ramsay Hunt Syndrome Type 2: A serious condition caused by the varicella-zoster virus that can lead to facial paralysis, ear pain, and vesicles in the ear, along with other symptoms. Early recognition and treatment are crucial.
Malignant Otitis Externa: Although more commonly associated with external ear canal infection, in diabetic or immunocompromised patients, it can present with vesicles and severe pain, requiring prompt medical attention.

Bullous Pemphigoid: An autoimmune disease that can cause blistering of the skin, including the ears, though it's less common in this location.
Pemphigus Vulgaris: Another autoimmune disease that causes blistering, which can rarely affect the ears.
Dyshidrotic Eczema (Pompholyx): Characterized by small, itchy blisters on the hands or feet but can occasionally appear on the ears.