Eczema/Contact Dermatitis: This condition is characterized by red, itchy, and inflamed skin, which can sometimes progress to open ulceration with serous drainage, especially if scratched or infected. The annular (ring-shaped) appearance can be seen in certain types of eczema.

Impetigo: A highly contagious skin infection that can cause red sores on the skin, which can burst and form light brown crusts. It often starts with a single spot that spreads, potentially forming annular patterns.
Psoriasis: An autoimmune condition that speeds up the life cycle of skin cells, causing cells to build up rapidly on the surface of the skin. The lesions can be red, scaly, and sometimes form annular patterns.
Dermatophyte Infection (Ringworm): A fungal infection of the skin that can cause a ring-shaped lesion, which is typically red, itchy, and can have a clear center. It can sometimes lead to secondary bacterial infections causing serous drainage.

Malignancy (e.g., Squamous Cell Carcinoma, Basal Cell Carcinoma): Although less common, skin cancers can present with ulceration and surrounding erythema (redness). It's crucial to consider this diagnosis, especially in non-healing lesions or those with atypical appearances.
Vasculitis: Inflammation of the blood vessels, which can cause a variety of skin manifestations, including ulcers and purpura (purple spots). Certain types of vasculitis can be life-threatening if not promptly treated.
Infectious Diseases (e.g., Lyme Disease, Syphilis): Certain infectious diseases can cause skin lesions that might resemble the described symptoms. For example, the initial stage of Lyme disease can present with a characteristic "bull's-eye" rash (erythema migrans), which is annular.

Pyoderma Gangrenosum: A rare skin condition that causes painful ulcers, typically starting as a small pustule that breaks down to form a progressively enlarging ulcer. It's often associated with systemic diseases.
Cutaneous Leishmaniasis: A tropical disease caused by a parasite, leading to skin lesions that can ulcerate. The lesions can have a variety of appearances, including annular forms.
Erythema Multiforme: An immune-mediated disorder that can cause target-like lesions on the skin, which can sometimes ulcerate. It's often triggered by infections or medications.