You’re probably at least marginally familiar with allergies. More than half of the U.S. population tests positive for one or more allergens, and they rank 5th among other leading chronic diseases in the country.

Most of the time, they happen in response to a common and usually harmless environmental substance, such as pet dander or various foods.

But some rare allergies are much more strange and confounding — to the extent that one wonders how it might even be possible to live with a few of them.

Here are five of the weirdest ones in existence.

Touch (Dermatographic Urticaria)

 skin-writingImage via wikimedia commons

One particularly odd allergy, called dematographic urticaria, is a disorder where the skin reacts to simple touch. The subsequent raised hives happen as a result of even slight pressure — it’s alternatively called “skin writing,” because people who suffer from this disorder can write on their skin with just the pressure of a fingernail. Researchers theorize this is because of out-of-control mast cells, which release histamines due to a flimsy membrane surrounding the cells.

The histamines cause swelling, which generally only lasts for 15 to 30 minutes (although with some people, it can last longer). These hives can be catalyzed even by clothing or from chairs, so it’s not an easy affliction to live with when untreated by daily doses of antihistamines. Notably, there’s a fairly sizable community of dermatographic urticaria sufferers online; in some instances, this allergy has even been used as a mode of artistic expression by people who have it.

Fitness (Exercise-Induced Anaphylaxis)

While you’ve probably heard some people say they’re allergic to fitness; believe it or not, there is such an allergy. It’s incredibly rare, however, and the symptoms are highly variable. Subsequently, this allergy often goes undiagnosed.

Essentially, though, physical exertion triggers a fairly serious allergic reaction within sufferers — it’s speculated that this generally happens in combination with taking certain medications or consuming particular foods prior to exercising. Manifestations of this allergy include extreme fatigue, itchy skin, hives, swelling, choking, nausea and vomiting, raised blood pressure, and (in some extreme cases) even death. Check out this firsthand account of the allergy, which was published in Runner’s World in 2006.

Sunlight (Solar Urticaria & PMLE)

 sunlightImage via Flickr by Social Media Sass

The beach is basically off-limits if you suffer from solar urticaria — you’ll break out in hives if you’re exposed to ultraviolet or UV radiation or (in some rarer cases) even visible light. While clothing offers protection, this isn’t always how it works for the more extreme manifestations of this disorder.  Sufferers can take antihistamines help the condition, and the hives generally disappear within approximately 30 minutes of getting out of the sun.

There’s also a condition called polymorphous light eruption (PMLE) that usually counts fair-skinned females among the ranks of its afflicted. While the symptoms and causes appear to be similar, these count as two separate allergies. Physicians generally recommend that people with PMLE use high-SPF sunscreens and that they track allergy symptoms whenever they appear.

Orgasms (POIS & Seminal Plasma Hypersensitivity)

Yes, it’s possible to be allergic to your own orgasms. Post orgasmic illness syndrome — where the body reacts negatively to the act of ejaculating — is suffered almost exclusively by men. Following the act of ejaculation, these men will suffer from fevers, exhaustion, running nose and stinging eyes, with symptoms lasting for nearly seven days. Medical tests have shown that this is the result of an allergy to their own semen; the illness is currently being treated in medical trials, where men are injected with their own semen.

A considerably larger segment of the nation’s female population suffer from a similar allergy to semen called seminal plasma hypersensitivity: Up to 40,000 of them, by some estimations. However, it’s still up in the air as to whether certain semen causes it, or if it’s all semen. There’s a range of different ways this disorder is treated, from condom use to desensitization through incremental exposure.

Water (Aquagenic Urticaria)

 waterImage via Flickr by AMagill

It might be difficult to believe that a human being could be allergic to water; after all, more than half of the human body consists of H2O. But aquagenic urticaria a real allergic disorder, nonetheless, albeit very rare. Exposure to water causes people with this condition to break out in red or white hives wherever their skin comes into contact with water.  The temperature or condition (hard, soft, etc) of the water seems to be irrelevant, and it appears to affect women most commonly.

All of this makes bathing, swimming, and being caught in the rain incredibly inconvenient for people who suffer from this disease. There are numerous treatments to lessen the symptoms of this disease, but none to fully eradicate it.

Aside from these five, there is a pretty impressive litany of odd and unusual allergies from with people suffer. These disorders only serve to show that the human body is indeed an intriguing mystery and, while medical science has come a long way in the last century, we still have a long way to go until we even come close to understanding all the things that affect our physical well-being.

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