Dry Skin (Xerosis): This is a common condition that can cause diffuse body pruritus, especially in dry environments or during winter months. The lack of significant past medical history and normal laboratory results supports this diagnosis.

Atopic Dermatitis: Although the patient has no past medical history, atopic dermatitis can present at any age. It is characterized by intense pruritus and can be widespread.
Psoriasis: Psoriasis can cause pruritus, although it typically presents with characteristic skin lesions. However, in some cases, the lesions might be subtle or overlooked.
Allergic Contact Dermatitis: Exposure to new soaps, detergents, or other allergens could cause a reaction leading to diffuse pruritus.
Hypothyroidism: Although the labs are reported as normal, hypothyroidism can sometimes present with nonspecific symptoms including pruritus, and thyroid function tests might need to be specifically ordered.

Hodgkin Lymphoma: Pruritus can be a presenting symptom of Hodgkin lymphoma, and it's crucial not to miss this diagnosis due to its significant implications.
Cholestasis: Intrahepatic or extrahepatic cholestasis can cause severe pruritus. Normal labs might not rule out early or mild cases, and specific liver function tests or bilirubin levels should be checked.
Multiple Myeloma: Although rare, multiple myeloma can present with pruritus among other symptoms, and it's a diagnosis that should not be overlooked.

Polycythemia Vera: A myeloproliferative disorder that can cause pruritus, especially after warm baths or showers.
Neurological Disorders (e.g., Multiple Sclerosis, Neuropathies): In some cases, neurological conditions can manifest with pruritus as a symptom.
Parasitic Infestations (e.g., Scabies, Pediculosis): Although typically associated with more localized symptoms, in severe cases or in immunocompromised patients, these infestations can cause diffuse pruritus.
Drug-Induced Pruritus: Certain medications can cause pruritus as a side effect, and a thorough medication history is essential.