Urticaria: This is the most common condition that presents with rash similar to hives. It is characterized by itchy, raised, and transient wheals that can appear anywhere on the body. The cause can be allergic, autoimmune, or idiopathic.

Atopic Dermatitis (Eczema): While not typically presenting as hives, atopic dermatitis can sometimes cause urticaria-like lesions, especially in acute phases. It's a chronic condition with dry, itchy skin, and is often associated with allergies and asthma.
Insect Bites or Stings: Reactions to insect bites or stings can mimic hives, especially if the reaction is severe. These are usually itchy and can vary in size.
Contact Dermatitis: An allergic or irritant reaction to substances coming into contact with the skin, which can sometimes appear similar to hives, especially in the acute phase.

Anaphylaxis: Although anaphylaxis is a systemic reaction that includes symptoms beyond skin rashes (such as difficulty breathing, rapid heartbeat, and a fall in blood pressure), it can initially present with urticaria-like rashes. Missing this diagnosis can be fatal.
Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN): These are severe skin conditions usually triggered by medications. They can start with symptoms similar to hives but rapidly progress to blistering and peeling of the skin, which can be life-threatening.
Mastocytosis: A condition where there's an accumulation of mast cells in one or more organs, which can cause hives-like symptoms among other systemic issues. It's crucial to diagnose to manage symptoms and prevent severe reactions.

Erythema Multiforme: A skin condition characterized by target lesions, which can sometimes be confused with hives. It's often triggered by infections or medications.
Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis): Characterized by fever, neutrophilia, and tender, erythematous skin lesions that can resemble hives. It's a rare condition that can be associated with infections, inflammatory bowel disease, or malignancies.
Autoimmune Progesterone Dermatitis: A rare condition in women that causes a cyclic skin rash, which can appear similar to hives, related to the menstrual cycle and sensitivity to progesterone.