Blepharitis: This condition is characterized by inflammation of the eyelids, often resulting in swelling, crusting on the eyelashes, and itchiness. The symptoms described are classic for blepharitis, which can be caused by a variety of factors including poor eyelid hygiene, allergies, or infections.

Allergic Conjunctivitis: This condition involves an allergic reaction to substances like pollen, dust mites, or pet dander, leading to itchy, watery eyes, and can sometimes cause swelling of the eyelids. The itchy sensation behind the ears could be related to an allergic reaction affecting multiple areas of the body.
Seborrheic Dermatitis: This is a skin condition that can cause scaly patches, red skin, and stubborn dandruff. It often affects oily areas of the body, such as the face, including the eyelids, and can lead to crusting and itchiness.
Eczema (Atopic Dermatitis): Eczema can cause itchy, inflamed skin, and can affect any part of the body, including the eyelids and the area behind the ears. It's known for its intense itch and can lead to crusting if scratched.

Orbital Cellulitis: Although less likely, this is a serious infection of the tissues surrounding the eye, which can cause swelling of the eyelid, among other symptoms. It requires prompt medical attention to prevent serious complications.
Herpes Zoster (Shingles): This viral infection can cause a painful rash and may affect the eye, leading to swelling and crusting. It's crucial to diagnose and treat shingles promptly to avoid complications like vision loss.

Demodex Infestation: Demodex mites can live on human hair follicles and are more commonly found in people with blepharitis. While rare, an infestation could exacerbate symptoms of eyelid swelling and crusting.
Rosacea: This condition can cause redness, acne-like symptoms, and sometimes affects the eyes (ocular rosacea), leading to symptoms that might include eyelid swelling and crusting. However, it's less directly associated with the specific combination of symptoms described.