Differential Diagnosis for a Well-Demarcated Skin Lesion Underneath the Eye

Single Most Likely Diagnosis

• Eczema (Atopic Dermatitis): This condition is characterized by itchy, inflamed skin that can be well-demarcated and erythematous. The intermittent flaking could be due to the natural fluctuation of eczema symptoms or the result of scratching, which can lead to further irritation and scaling.

Other Likely Diagnoses

• Seborrheic Dermatitis: This is a common skin condition causing a red, itchy, and flaky rash, typically on the scalp, but it can also occur around the eyes. The description of the lesion being slightly raised, erythematous, and flaking intermittently aligns with seborrheic dermatitis.
• Contact Dermatitis: An allergic reaction or irritation from substances like makeup, skincare products, or even certain metals in jewelry could cause a well-demarcated, erythematous lesion that flakes. The location under the eye makes this a plausible diagnosis due to the common use of cosmetics in this area.
• Keratosis Pilaris: Although more common on arms and legs, keratosis pilaris can appear on the face, causing small, rough, sandpapery patches that might fit the description given. However, it's less likely to be as localized or under the eye specifically.

Do Not Miss Diagnoses

• Basal Cell Carcinoma: While less common in the description provided, basal cell carcinoma can present as a well-demarcated, erythematous lesion. The potential for intermittent flaking could be mistaken for a benign condition, but any new or changing skin lesion warrants consideration of skin cancer.
• Squamous Cell Carcinoma: Similar to basal cell carcinoma, squamous cell carcinoma is a type of skin cancer that could present with a raised, erythematous lesion. It might also exhibit flaking or crusting, making it crucial not to miss this diagnosis.

Rare Diagnoses

• Discoid Lupus Erythematosus: A chronic skin condition characterized by inflammation and scarring type lesions, typically on the face. While it could present with well-demarcated, erythematous lesions, it's less common and usually associated with other systemic or cutaneous manifestations of lupus.
• Granuloma Faciale: A rare skin condition that causes single or multiple, well-defined, erythematous to purple plaques or nodules, typically on the face. It could fit the description but is relatively rare and might require a biopsy for diagnosis.