Five of the Strangest Allergies Confirmed by Science

Allergies are the result of the body's adaptive immune system misidentifying a chemical signature as foreign and/or harmful, recruiting immune factors like immunoglobulin E (IgE) to fight the perceived threat. While allergies to foreign bodies (such as pollen) or foods and medications are common, there seems to be no limit to what the immune system is capable of fighting.

Sunlight Allergy
As strange as it seems, it's possible to be allergic to the sun! "Solar urticaria" is the term for hives induced by sunlight. Ultraviolet radiation or even some strong visible light can induce painful, itchy rashes in sufferers of this condition. While research is ongoing into the mechanism of this condition, the most complete model suggests that an endogenous molecule is modified by UV light into a structure the body has become sensitized to, thus incurring the histamine reaction which provokes the itchy rash associated with allergies.

Cold Rash
Even less well-understood than solar urticaria is cold urticaria, whereupon exposure to cold results in the formation of taut, raised wheals in a patchy distribution over the skin, often along with swollen hands and feet. In this case, doctors are still unsure what biochemical factor is responding to the cold and causing the histamine release.

Skin-Writing
Some patients can experience an allergic skin response to touch so localized they can actually write on their skin! Called dermatographism, this allergy is provoked by an overzealous reaction to stimulation by mast cells, which release histamine at the location of the touch to provoke an exceptionally specific response such that words and shapes can be "written" in raised welts with the touch of a fingernail.

Exercise Urticaria
It sounds like a thin excuse to stay on the couch, but some people actually experience an allergic reaction to exercise. The physiological processes occurring during exercise involve sweating and skin flushing as blood is drawn to the surface, which in rare cases can trigger an incidental histamine release, producing hives and swelling.

Gold Allergy
The first assumption upon hearing of a "gold allergy" is to assume the piece has been alloyed with nickel, a common metal allergen. However, there exists a small subject of the population that is indeed sensitive to pure gold. Gold allergies present with a telltale subtype of skin irritation called dyshidrotic eczema, characterized by clustered serous vesicles. This allergy is often difficult to diagnose, as symptoms may take weeks or months to manifest.

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