Kidney infections can be, and sometimes are, lethal. That UTI you had that resolved without antibiotics? Well, you got lucky, assuming you’re sure the initial infection cleared up on its own. Most kidney infections start out as urinary tract infections. It’s most usually caused by E. Coli, which is present on most surfaces, including other people’s skin. E. Coli is usually harmless unless it manages to infect, and if you notice that you get UTIs whenever you’re sexually active, a very common cause is a sensitivity to the bacteria natural to your partner’s body; you can reduce your chances of an infection by washing before sex and making sure you go pee as soon as you’re done to literally rinse out your urethra. Condoms and dental dams can also help depending upon your body chemistry, but not always. Properly using a bidet (they come in portable travel-size models now for like, $30, Americans) can also drastically help reduce your risk of an infection.

The problem is that the renal (pee) system is all connected by tubes and hoses that can be very easy for bacteria to climb. Here’s a very generic, non-gendered diagram:

(source)

Regardless of what you’ve got from a reproductive standpoint, that’s pretty much it! Same wiring and everything, save for that people who are AFAB aren’t typically born with prostates, which isn’t part of the renal system at all. People with short urethras (AFAB people, intersex, endocrine syndrome, etc) contract UTIS and bladder infections. AFAB or AFAB-similar people have a 40% likelihood of contracting a common UTI at least once in their lives. AMAB people only have about a 12% chance. The difference is so drastic because said AMAB people have pretty average external genitalia and therefore a much longer urethra than average for bacteria to try to survive colonizing. Drinking water and going to the bathroom regularly are highly effective at preventing a renal infection, because the bacteria literally has to climb its way from the urethra to the kidneys. Urinating helps to wash it out. Depending upon your immune system, it can take days or even weeks before the bacteria reaches your kidneys if that’s what’s going to happen.

Not only are kidney infections incredibly painful (There Will Be Blood), but those yellow nodules on top of the kidneys in that diagram I posted up there? Those are your adrenal glands. Where all of your adrenaline comes from. Those major veins and arteries also can give the bacteria unmitigated access to the bloodstream, which generally leads to sepsis, shock, and death. If your adrenal glands are infected, it can cause them to release dangerous amounts of adrenaline that can stress, damage, and even cause the heart to stop.