Dear Matthew Alice: My friends and I have discovered we all have something in common: frequent anal itching. My roommate explained to me this was caused by bugs that could be seen if a piece of tape were applied to the area, which she learned in biology class. Matt, how can this be? I am a very sanitary person who showers daily and would please like a solution to this problem. — Jennifer, Pacific Beach

Brave of you to air your butt itch in public so we all can benefit from Dr. Alice’s two-bit advice. Scotch Tape is the time-honored diagnostic tool for a rude lower-intestinal parasite called pinworm. Apply tape to butt, then to glass slide, and look for pinworm eggs under a microscope. Mom pinworm is about 3/8-inch long, dad is about a tenth that size. They usually get in through your mouth, then whip through your digestive tract to your lower intestine, where they take up residence. Finally, one night while you’re snoozing away in bed, mom pinworm decides it’s time to lay eggs. She scrunches her way outside and lays ’em in the folds of skin around your anus. Then she dies. Then you scratch.

But pinworm is only one of the possible causes of pruritus ani, the medical term for your condition. You could have a fungal, bacterial, or yeast infection; an allergy to foods or soaps or perfumed toilet paper; or maybe anal fissures or excessive sweating or maybe you are overzealous about anal hygiene. Sneakiest of all, one of the most common reasons for butt itch is neurodermatitis from too much butt scratching. Say you had some temporary itching condition and you scratched the heck out of it. Scratching can injure the delicate tissue, which builds up a thickened skin layer as protection. But this also itches, so the scratching continues. By the way, hemorrhoids themselves don’t itch, but skin damage from excessive use of over-the-counter painkiller creams can cause neurodermatitis. Get your butt to a doctor, J.