An allergy is reaction that occurs when the body's immune system overreacts to a substance that is normally harmless.
This substance is called an allergen. The cause of most people’s allergies is not known. An allergy usually begins with sensitisation when the person is exposed to an allergen, and symptoms vary according to the type of allergy.
If you thought being allergic to nuts, milk, wheat etc. was strange enough, that's just the tip of the allergy iceberg. There is a British woman who is – wait for it – allergic to water. 26-year-old Rachel Prince has to avoid absolutely all contact with water because even the tiniest drop on her skin can cause excruciating pain.
This condition is called Aquagenic Pruritus and even a drop of saliva can bring about an extremely itchy reaction.
According to the Daily Mail: "The condition is so rare it’s believed Rachel is one of only about 35 people in the world who suffer from it."
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2. Kissing allergy
Simply sharing a kiss with your loved one can cause you to break out in hives, a rash, get itchy eyes, blisters on the eyelids, puffy lips, wheezing and cause you difficulty in breathing.
This allergy doesn't mean you're allergic to the person's lips or tongue, but you're allergic to something you picked up in their saliva, such as food particles or undissolved medicine.
3. Touch allergy
This allergy is called dermographism and is a type of physical urticaria (hives). Dermographism literally means 'writing on the skin' - if you scratched your skin with something sharp, you could write on it. But it's the pressure you put on your skin that actually causes the allergy.
Touch allergy can also occur if you wear tight clothing or even when you dry yourself off after a shower. The good news is dermographism only affects about 4% of the world's population and it usually goes away on its own after about 15 to 30 minutes.
4. Semen allergy
Sex allergy should more correctly be called semen allergy and it occurs in both men and women. It is estimated that approximately 12% of women suffer from an allergy to semen. It happens when the body's immune system overreacts to the presence of semen. The white blood cells mistakenly identify proteins in the semen as harmful invaders (such as bacteria or viruses) and attack it.
Common symptoms include burning, itching, and swelling of the genitals or areas of the skin that come into contact with the semen. Reactions can however be far more life-threatening with sufferers going into anaphylactic shock.
Read: Allergy to semen after orgasm a rare illness
5. Wood allergy
While many people are allergic to certain types of wood or sawdust, there are cases where people are allergic to all types of wood in any form, whether it's sawdust or solid wood.
Along with wood allergies comes the fact that you can't touch paper or even use a pencil, and you certainly can't be a carpenter or woodcutter. According to Oddee.com the allergy can be so severe that 'it can cause the skin to look as if it were burned.'
Most cases of wood allergies cause symptoms such as skin irritation, coughing, sneezing, and hives.
6. Exercise allergy
Think you're allergic to exercise? It can be more than a mental 'thing' as and thousands of people are suffering from it.
According to Allergies About.com exercise-induced anaphylaxis (EIA) is a severe allergic reaction caused by physical exercise. One type occurs after eating food within two hours of exercise and the other occurs independent of food. In either case, you should stop exercising, but you can prevent the food-related type by not eating before exercise.
Symptoms of this allergy are fatigue, warmth, itching, redness of the skin, followed by large hives, collapse and unconsciousness.
Read: Common allergy triggers
7. Sun allergy/Solar urticaria (SU)
This allergy, also called photosensitivity, is a rare condition that occurs when the body's immune system overreacts to sunlight. Exposure induces a case of urticaria or hives that can appear on both covered and uncovered areas of the skin.
It appears within 30 minutes of sun exposure and clears up within minutes of getting out of the sun.
8. Electricity allergy
This is also called electrosensitivity, and sufferers are sensitive to electric fields generated by products such as cell phones, microwaves, computers, and power lines.
Symptoms of electricity allergy include headache, ringing in the ears and fatigue. Do you have any of these symptoms?
Could you be like the 39-year-old Debbie Bird from England who is so sensitive to any electromagnetic field that if she goes anywhere near one, she develops a painful skin rash and her eyelids swell to three times their normal size?
According to Everyday Health, several studies have been done to see if electrosensitivity really exists, and almost all of the studies have come up empty. But what is happening to Debbie?
Read: Is electrosensitivity simply due to the 'nocebo' effect? I.e., if you think you'll get sick from it, you do.
9. Leather shoe allergy
Just about everyone wears leather shoes, but a small portion of the population can't - they're allergic to leather and it can be so severe that it feels like you're wearing shoes made of stinging nettle.
The only way out is to either wear really thick socks, or shoes made out of cloth or plastic.
10. Money allergy
You may think those dirty banknotes are to blame, but in fact it's the coins. Just by touching them you can break out in a rash with all the usual suspects such as itching, redness, swelling and unsightly dry patches.
Experts say if this happens you could have a reaction to nickel. Nickel is a metal alloy and is used to make a number of everyday items such as clothing zippers, jewellery, bra hooks, pens, cigarette lighters, cellphones and your glasses' frames.
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Find out more: about allergies on our allergy centre.
Sources: Daily Mail, Health24, Everyday Health, Oddee.com, Express