Most kidney infections will start with bacteria that travel up the urinary tract to the bladder; the infection can then make its way to the kidneys. Because women have a shorter urethra than men, they’re at higher risk for urinary tract infections (UTIs)—and that leaves them more vulnerable to kidney infections. Frequent intercourse or a new partner may also increase a woman’s risk, says Nicole Ali, MD, a nephrologist at NYU Langone. As the body fights the infection, red blood cells can end up in your urine, she says. Don’t miss these other warning signs your kidneys are in big trouble.