Contact Dermatitis: This is a common condition that can occur after surgery due to irritation from surgical tapes, antiseptics, or other products used during the procedure. The rash typically appears as red, itchy, and blistered skin at the site of contact.

Allergic Reaction to Medication: Patients may develop an allergic reaction to antibiotics or other medications administered during or after surgery, leading to a rash.
Surgical Site Infection: Bacterial, viral, or fungal infections can cause a rash at the surgical site, often accompanied by other symptoms like redness, swelling, and increased pain.
Irritant Dermatitis: Similar to contact dermatitis but caused by substances that irritate the skin rather than an allergic reaction, such as soap, shampoo, or certain components of surgical preparations.

Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN): Although rare, these are life-threatening conditions that can be triggered by medications. They cause widespread skin necrosis and detachment, often preceded by a rash.
Necrotizing Fasciitis: A severe infection that can cause a rash and rapidly progresses to necrosis of the skin and underlying tissues, requiring immediate medical attention.
Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS): A severe drug reaction that can present with a rash, fever, and systemic symptoms, potentially involving multiple organs.

Erythema Multiforme: An immune-mediated disorder that can be triggered by infections or medications, characterized by a distinctive target-like rash.
Fixed Drug Eruption: A type of drug reaction that causes a rash at the same site each time the offending drug is taken.
Graft-Versus-Host Disease (GVHD): In patients who have undergone organ or bone marrow transplantation, GVHD can cause a rash among other systemic symptoms, as the immune cells from the graft react against the host's tissues.