Acute Urticaria: This is the most common cause of full body hives, often triggered by allergic reactions to foods, medications, or infections. It presents with sudden onset of itchy, raised wheals that can appear anywhere on the body.

Chronic Urticaria: Similar to acute urticaria but lasts more than 6 weeks. Causes can be autoimmune, allergic, or idiopathic.
Insect Sting or Bite Allergy: Allergic reactions to insect stings or bites can cause full body hives, especially in individuals with a known history of such allergies.
Drug Allergy: Many medications can cause allergic reactions leading to full body hives, including antibiotics, NSAIDs, and blood pressure medications.

Anaphylaxis: A severe, life-threatening allergic reaction that can cause full body hives along with other symptoms like difficulty breathing, rapid heartbeat, and a drop in blood pressure. Immediate medical attention is required.
Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN): A severe skin condition usually caused by medications, leading to widespread skin lesions and detachment. It's rare but can be fatal if not promptly treated.
Mastocytosis: A condition characterized by the accumulation of mast cells in the skin and other organs, which can cause hives, itching, and anaphylaxis.

Autoimmune Disorders (e.g., Lupus, Rheumatoid Arthritis): Certain autoimmune diseases can cause urticaria as part of their symptomatology.
Parasitic Infections (e.g., Giardiasis, Strongyloidiasis): Some parasitic infections can trigger allergic reactions, including full body hives.
Malignancy (e.g., Lymphoma, Leukemia): In rare cases, full body hives can be a symptom of an underlying malignancy.
Urticarial Vasculitis: An inflammation of the blood vessels that can cause hives, but it's a rare condition and usually presents with other systemic symptoms.