Medications and other chemicals
Triggers:

Many drugs can cause pseudoallergic reactions by directly activating mast cells or stimulating other non-immunologic pathways, leading to the release of inflammatory mediators like histamine, including:

Painkillers, antibiotics, chemotherapeutics, steroids, corticosteroids, anticonvulsants, monoclonal antibodies, and even laxatives and tap water have been linked to triggering CARPA.

NSAID-Exacerbated Cutaneous Disease (NECD), where NSAIDs worsen pre-existing chronic urticaria.

NSAID-Induced Urticaria/Angioedema (NIUA) in individuals without an underlying chronic condition.

Opioids: Drugs such as morphine and codeine can directly activate mast cells, causing the release of histamine and resulting in flushing or itching.

Radiocontrast media: The dyes used in some medical imaging tests can directly induce mast cell activation.

Vancomycin: The antibiotic vancomycin can cause "red man syndrome," a pseudoallergic reaction characterized by flushing and a rash, particularly around the face, neck, and upper body.

Anesthetics: Certain agents used in general anesthesia, particularly neuromuscular blocking agents, can cause severe pseudoallergic reactions. 

Nanomedicines: This broad category encompasses liposomal drugs, certain cancer chemotherapies and antifungal medications, micellar formulations, and other nanoparticle-based therapies.

Biological Therapies: Monoclonal antibodies, used to treat various conditions including cancer and autoimmune diseases, can induce CARPA.

Intravenous Iron Formulations: Certain types of intravenous iron used to treat anemia are known to be associated with these reactions.

Radiocontrast Media: The dyes used in imaging procedures, such as CT scans, can also be a trigger.

Allergic reactions to corticosteroids:

These responses can manifest immediately, within one hour of administration, or be delayed, emerging days afterward.

Clinical symptoms may include rash, swelling, respiratory difficulty, dizziness, or, in severe instances, cardiovascular collapse.