By Melissa Dahl

For one 21-year-old muscle man, the quest to build a perfect body ended in grotesque, lifelong scars.

Doctors were shocked when the young man came into their Dusseldorf clinic with one of the worst cases of acne conglobata any of them had ever seen: His chest and upper back were canvassed in craterlike ulcers and abscesses oozing with pus.

“He had these deep, ulcerating lesions with bloody crusts,” says Dr. Peter Arne Gerber, a dermatologist who treated the young man at Heinrich Heine University in Dusseldorf, Germany. Adding insult to injury, the poor young man’s sperm count had plummeted and his testicles were in a sad little shrunken state.

By Melissa Dahl

Does all that exertion on the elliptical machine make you nauseous? Have you ever been convinced that if you spend even one more minute on the treadmill, you will actually die? Maybe it’s not all in your head.

A few people are actually allergic to exercise, and in very rare cases, a sweaty workout could be enough to kill them. What an awesome excuse to skip the gym!

Exercise-induced anaphylaxis is a fairly rare condition which can cause hives, fainting, vomiting and difficulty breathing during a workout, and the symptoms can last up to four hours after it. In some cases, it can be triggered by certain foods eaten before exercise, like peanuts, shellfish, eggs or even, in two reported cases, celery. But this isn't just your average food allergy, an expert explains.

"These are people who will not have this reaction unless they exercise right after eating this food," says Dr. Jacqueline Eghrari-Sabet, an allergist in private practice in Montgomery Village, Md., and a spokeswoman for the American Academy of Allergy, Asthma and Immunology. "Eating shellfish and sitting there? Nothing. But eating shellfish and exercising? For these people, it's bad news."

By Melissa Dahl, health writer

It’s a gross-out skill little brothers seem to be born with – a knack for turning their eyelids inside out, effectively freaking out all the ladies in their lives.

A fun, freaky trick, sure. But what if you couldn’t help flipping your lids? Some eyelids among us have minds of their own, flipping and flopping inside out whenever they please.

Those with a condition called floppy eyelid syndrome have lids that lack a normal amount of elastin, making the thin skin super stretchy. Grossing out their peers is totally out of their control – their eyelids can turn inside out spontaneously. In some cases, the upper lid can stretch all the way to the eyebrow, and both the upper and lower lids can be pulled forward as much as two centimeters. (Doesn’t seem like very much? Try seeing how far yours will go.)

By Melissa Dahl, health writer

Does the very sound of a Fergie tune make you feel a bit ill? Maybe it’s not all in your head.

For Stacey Gayle, it was hip-hop artist Sean Paul who was making her sick – specifically his 2005 hit “Temperature.” Before the Jamaican rapper could promise to keep her warm, to shelter her from the storm, Paul had sent Gayle into a seizure.

When Gayle collapsed at a barbecue immediately after a Sean Paul song started playing, the 25-year-old started to put the pieces together. She brought her iPod to a medical center and played a Sean Paul song for her doctors – and suffered through three seizures shortly after.