Urticarial vasculitis: This condition is characterized by inflammation of the blood vessels and can present with urticaria (hives) followed by bruising due to the damage to the blood vessels. It's a common cause of bruising after urticaria and should be considered first due to its direct association with the symptoms described.

Henoch-Schönlein purpura (HSP): Although more commonly associated with palpable purpura, HSP can sometimes present with urticaria-like lesions that evolve into bruises. It's an important consideration, especially in children.
Insect bite or sting reactions: Certain insect bites or stings can cause an allergic reaction leading to urticaria, which may then develop into bruising due to the severity of the reaction or secondary infection.
Autoimmune disorders (e.g., lupus, rheumatoid arthritis): These conditions can cause a wide range of skin manifestations, including urticaria and subsequent bruising, due to the autoimmune nature of the disease affecting blood vessels and skin.

Thrombocytopenia or coagulopathy: Conditions affecting platelet count or function, or the coagulation cascade, can lead to easy bruising. While they might not directly cause urticaria, the presence of bruising after minor skin reactions could be a sign of an underlying issue with blood clotting.
Malignancy (e.g., leukemia, lymphoma): Certain cancers can cause a variety of skin symptoms, including urticaria and bruising, due to either direct skin involvement or secondary effects on the blood and immune system.
Infections (sepsis, endocarditis): Severe infections can lead to a range of systemic symptoms, including skin manifestations like urticaria and bruising, especially if there's an associated coagulopathy or vasculitis.

Ehlers-Danlos syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. While rare, it could potentially lead to easy bruising and skin hyperextensibility, which might be mistaken for urticaria.
Pseudoporphyria: A condition that can mimic porphyria cutanea tarda, with skin blistering and fragility leading to bruising, potentially after minor trauma or sun exposure, which might be confused with urticaria in some cases.
Amyloidosis: A condition characterized by the deposition of amyloid (a particular type of protein) in various tissues of the body. Skin manifestations can include easy bruising and petechiae, potentially following urticaria-like reactions, although this would be quite rare.