Seborrheic Dermatitis: This condition is characterized by a crusty, itchy outer ear and can sometimes present with a yellow slough due to the buildup of dead skin cells and oil. It's a common condition that affects areas rich in sebaceous glands, like the ears.

Otitis Externa (Swimmer's Ear): An infection of the outer ear canal, often caused by bacteria or fungi, which can lead to symptoms like itchiness, redness, and a yellowish discharge or slough. The crusty appearance can be due to the body's response to the infection.
Eczematous Dermatitis (Atopic or Contact): This can cause itchy, crusty lesions on the outer ear, potentially with a yellow slough if there's a secondary infection. Allergens or irritants can trigger this condition.
Psoriasis: Although less common on the outer ear, psoriasis can cause itchy, scaly plaques that might appear crusty and could potentially have a yellow slough if infected.

Malignant Otitis Externa: A severe infection that can spread to the temporal bone and skull base, more common in diabetic or immunocompromised patients. It presents similarly to otitis externa but is much more dangerous and requires prompt treatment.
Squamous Cell Carcinoma: A type of skin cancer that can appear as a crusty, non-healing lesion on the outer ear. It's less common but critical to diagnose early due to its potential for metastasis.

Keratosis Obturans: A condition where a plug of desquamated skin accumulates in the ear canal, potentially causing symptoms similar to otitis externa, including itchiness and a crusty appearance.
Relapsing Polychondritis: An autoimmune disorder that can cause inflammation and destruction of cartilaginous structures, including the outer ear, leading to crusty lesions and other symptoms. It's rare and often associated with other systemic symptoms.