Seborrheic Dermatitis: This condition is characterized by a red, scaly, and greasy appearance, often affecting the outer ear (pinna). The patient's symptoms of redness, scaliness, and greasiness, along with some yellow discharge, are classic for seborrheic dermatitis. The partial response to over-the-counter (OTC) hydrocortisone also supports this diagnosis, as seborrheic dermatitis often responds to topical corticosteroids.

Contact Dermatitis: This could be either irritant or allergic in nature. The patient's symptoms could be due to an allergic reaction or irritation from a new product (e.g., hair dye, shampoo, or earrings), which would cause redness, itching, and possibly a scaly appearance.
Eczema (Atopic Dermatitis): Although less common in adults as a new diagnosis, eczema can cause itching, redness, and scaling. The involvement of the outer ear could be part of a more generalized condition or a localized reaction.
Psoriasis: Psoriasis can affect the ears, causing red, scaly patches. The greasiness and yellow discharge might not be as typical, but psoriasis can have various presentations, including on the ears.

Cellulitis: Although less likely given the patient's response to hydrocortisone, cellulitis is an infection of the skin and subcutaneous tissues that requires prompt antibiotic treatment. It can present with redness, swelling, and warmth, and it's crucial not to miss this diagnosis due to its potential for serious complications.
Malignancy (e.g., Squamous Cell Carcinoma): Rarely, a lesion on the ear could be malignant. While the symptoms described don't strongly suggest cancer, any persistent or unusual skin lesion, especially in sun-exposed areas like the ear, warrants careful examination and possibly a biopsy if it doesn't respond to standard treatments.

Pityriasis Rosea: This condition can cause a rash that might involve the ears, but it typically starts with a "herald patch" followed by a wider rash on the body, which doesn't seem to match this patient's presentation.
Keratosis Obturans: A condition where a plug of keratin forms in the ear canal, potentially causing itching and discomfort, but it's more related to the ear canal than the outer ear.
Relapsing Polychondritis: An autoimmune condition that can cause inflammation of the cartilage, including that of the ears, leading to redness, swelling, and potentially deformity. However, this condition is rare and usually involves more systemic symptoms or other areas of cartilaginous involvement.