Eczema (Atopic Dermatitis): Given the patient's history of being treated with steroid creams and the rash's tendency to come and go, eczema is a strong candidate. It's a chronic condition characterized by inflammation of the skin, often appearing as itchy, red, and swollen patches.

Psoriasis: This is another chronic skin condition that can cause a rash, often appearing as thick, scaly, red patches. The fact that the rash comes and goes and has been treated with steroid creams (which are sometimes used for psoriasis) makes this a plausible diagnosis.
Contact Dermatitis: This condition occurs when the skin comes into contact with an allergen or irritant, causing a rash. Given the rash's location on the legs and its intermittent nature, contact dermatitis is a possibility, especially if the patient has recently changed soaps, detergents, or has been exposed to new substances.
Keratosis Pilaris: A condition characterized by small, rough patches on the skin, often on the legs. While it doesn't typically come and go as described, it's common and could be considered, especially if the rash is more of a texture change than an inflammatory one.

Cutaneous T-Cell Lymphoma (Mycosis Fungoides): Although rare, this is a type of skin cancer that can present with a rash that resembles eczema or psoriasis. It's crucial to consider this diagnosis to avoid missing a potentially deadly condition.
Infectious Diseases (e.g., Lyme Disease, Syphilis): Certain infectious diseases can cause skin rashes. While less likely, these conditions can have serious consequences if not treated promptly.
Autoimmune Disorders (e.g., Lupus): Systemic lupus erythematosus and other autoimmune diseases can cause skin rashes among other symptoms. These conditions require early diagnosis and treatment to prevent serious complications.

Sarcoidosis: A condition that can cause skin rashes, among other symptoms, due to the formation of granulomas in various parts of the body. It's less common but should be considered if other diagnoses are ruled out.
Pityriasis Rubra Pilaris: A rare skin disorder characterized by constant inflammation and scaling (exfoliation) of the skin. It can resemble psoriasis but has distinct features, including the formation of reddish-orange patches and scaling.
Dermatomyositis: An inflammatory disease characterized by skin rash and muscle weakness. The rash typically appears as a purple rash on the eyelids, knees, and elbows, but it can have a varied presentation.