Eczema (Atopic Dermatitis): This is the most common condition associated with a dry, scaling, itching rash. It's a chronic condition characterized by inflammation of the skin, and its symptoms match the description provided.

Psoriasis: A chronic autoimmune condition that speeds up the life cycle of skin cells, causing cells to build up rapidly on the surface of the skin. The extra skin cells form scales and red patches that itch or burn.
Seborrheic Dermatitis: A condition causing scaly patches, red skin, and stubborn dandruff due to an oily scalp. It can also occur on oily areas of the body, such as the face.
Contact Dermatitis: A type of inflammation of the skin that occurs when the skin comes into contact with an irritant or allergen, leading to a dry, scaling, itching rash.

Scabies: A contagious skin infestation by the mite Sarcoptes scabiei, characterized by intense itching and a pimple-like skin rash. Missing this diagnosis could lead to prolonged suffering and spread to others.
Lichen Planus: An inflammatory condition that affects mucous membranes inside the mouth and can also affect the skin, causing an itchy, scaling rash. It's less common but important not to miss due to its potential impact on quality of life.
Bullous Pemphigoid: A rare skin condition characterized by the formation of blisters, which can start as an itchy, scaling rash. It's crucial to diagnose early to prevent severe blistering.

Pityriasis Rubra Pilaris (PRP): A rare skin disorder that causes constant itching, scaling, and redness. It can start at any age and is characterized by small, pointed bumps on the skin.
Ichthyosis: A group of skin conditions that result in dry, scaly, and thickened skin. While not typically itchy in all forms, some types can cause significant discomfort and itching.
Keratosis Pilaris: A condition that causes small, rough patches on the skin, often on the arms, legs, buttocks, and cheeks. It can sometimes be itchy, especially in dry environments.