Cat urine, especially that of un-neutered males, might smell particularly rancid or foul to the human nose. To other male cats, it might smell similar, and to unaltered female cats, it might seem like a perfume. There are several reasons for this.
Hormones in the cat's urine serve as a reminder to other animals in the area this is his territory. Those same hormones also attract females that might be ready to mate. This is usually the case with a behavior called "spraying," instead of simple urination.
Urea is the main compound urine is composed of. When left to sit, it has a distinctive ammonia smell.
An underlying medical issue might cause an increase or change in the smell of a cat's urine. Cystitis, urinary tract infections and urethral blockage are common conditions that might have this effect.
Cats that are fed lower quality food that contain more fillers will have waste products in their urine that can cause an unpleasant odor. Malnutrition can also cause cat urine to smell rancid.
A regular veterinary examination will rule out any medical problems. It can also determine if the urine is abnormally strong smelling. Neutering will in all but about 13 percent of cases eliminate the most potent smelling urinary behavior of male cats.