Everyone knows you can be allergic to things like peanuts, bees, and cats. For people with such allergies, they can often get through life in relative safety by simply avoiding their triggers. But some unfortunate folks have rare allergies to things that are nearly impossible to avoid, like water and sunlight. Here are a few of the weirdest triggers known to drive the immune system into an unhelpful frenzy.
In 2016, the BBC detailed the tragic story of Rachel Warwick, a woman unable to even sweat without developing red welts on her skin. Warwick is one of the few people in the world known to have something called aquagenic urticaria (urticaria being the medical term for hives). Though her body doesn’t overreact to the water stored inside her cells, skin contact with any outside source of water — no matter the temperature or how distilled it is — can cause an intensely painful and itchy sensation that lasts for hours. Scientists don’t know much about why or how the rare condition happens, though it is known to affect women more than men, and symptoms tend to emerge in puberty.
There are people who develop hives after experiencing vibrations on their skin. Aside from hives, sufferers of vibratory urticaria can experience flushing, headaches, and a metallic taste in the mouth following exposure. Though these symptoms only last for up to an hour, people can experience multiple episodes a day. Triggers can include rubbing a towel on your skin, riding a bike, or even clapping your hands. Unlike aquagenic urticaria, researchers have been able to discover an inherited mutation that explains at least some cases.
Cold temperatures can be another cause of an immune freakout. We recently reported on a 37-year-old man who nearly died from anaphylaxis after he stepped out of a hot shower. Doctors believe the episode was triggered by his sudden exposure to cold air in the bathroom, a severe version of the hives he had begun experiencing when he moved to chilly Colorado from tropical Micronesia. Some cases of this allergy can be explained by a rare mutation passed down in families, but most remain unexplained.
An increasing but still-small number of people in the U.S. have developed an allergy to red meat. Unlike other allergies, the cause of this newfound aversion seems to be transmissible — the result of a bite from the Lone Star tick. The allergy isn’t to red meat itself but a sugar found in the muscles of most mammals (but not humans) called alpha-gal. Somehow, the tick’s bite sensitizes a person’s immune system into overreacting to alpha-gal, the way it does in a person allergic to peanuts, for example. Unlike many “classic” food allergies (where an exposure to peanuts quickly leads to symptoms within minutes, for example), symptoms of a meat allergy can take hours post-exposure to show up.
Another form of physical urticaria can be caused by the sunlight, known as solar urticaria. People with this condition develop distinct red welts within minutes of exposure to the sun, regardless of the outside temperature. This is in contrast to heat rash, a commonly misattributed condition caused by sweat ducts that have become clogged. Other kinds of physical urticaria tend to involve an overreaction by certain immune cells to a stimulus like cold or vibration, but solar urticaria might be caused when photosensitive chemicals in the body are created in response to UV radiation, which then somehow trigger an unwarranted antibody response.
You might be thinking that this is about an allergy to latex, a common material used in condoms. But this is actually about an even stranger condition — people who develop an immune overreaction to semen. Known as semen allergy or seminal plasma hypersensitivity, the culprit is likely due to proteins in the semen, not the sperm themselves. The condition can be managed through sticking to protected sex. But in at least one case study, doctors did seem to desensitise the woman’s reaction by first exposing her vagina to her partner’s semen, then prescribing a regular dose of sex to the couple every 48 hours.