Urinary Tract Infection (UTI): A common cause of hematuria (blood in urine) without pain, especially in women. UTIs can cause inflammation and irritation to the bladder and urinary tract, leading to bleeding.

Kidney Stones: Although often associated with pain, small stones may not cause significant discomfort and can still lead to bleeding.
Benign Prostatic Hyperplasia (BPH): Enlargement of the prostate gland can cause urinary retention and bleeding, especially in older men.
Menstrual Contamination: In women, menstrual blood can contaminate a urine sample, especially if collected during menstruation.

Bladder Cancer: Although less common, bladder cancer can present with painless hematuria and is critical to diagnose early for effective treatment.
Kidney Cancer: Similar to bladder cancer, kidney cancer can cause hematuria without pain and requires prompt diagnosis.
Sickle Cell Disease or Trait: Certain conditions like sickle cell disease can cause hematuria due to sickling in the kidney, which might not always be painful.

Alport Syndrome: A genetic disorder affecting the type IV collagen in the kidneys, leading to hematuria, often without pain.
Goodpasture Syndrome: An autoimmune disease causing inflammation in the kidneys and lungs, which can present with hematuria.
Nephrocalcinosis: A condition characterized by calcium deposits in the kidneys, which can cause hematuria, usually without significant pain.
Renal Artery or Vein Thrombosis: Although more commonly associated with acute pain, in some cases, especially in patients with risk factors like nephrotic syndrome, these conditions might present with painless hematuria.