What is the Rarest Allergy?

Allergies are a common problem that affect millions of people around the world. In the United States, more than 50 million people have allergies each year [*]. Most people know about allergies to pollen, dust, and pet dander, but some allergies are much rarer and more surprising.

Imagine having allergic reactions to water, sunlight, or even your own sweat. These unusual allergies may sound strange, but they are real and can make everyday life difficult.

In this article, you’ll learn about some of the rarest allergies in the world, what causes them, and how people manage their symptoms.

What is the Rarest Allergy?

Aquagenic urticaria, also known as a "water allergy," is one of the rarest allergies in the world. When people with this condition come into contact with water — whether it's from a shower, rain, or even sweat — their skin develops red, itchy hives [*].

Doctors aren’t exactly sure what causes this allergy. Some believe it happens because the allergy cells in the skin (called mast cells) react to the temperature changes that occur with coming into contact with water. Also, possibly even chemicals in the water might trigger these cells. What we do know is that this condition is somewhat uncommon.

The symptoms of aquagenic urticaria appear within minutes of water touching the skin. Itching, redness, and painful welts can last anywhere from 30 minutes to several hours. This makes daily activities like bathing or swimming very difficult.

There are treatments for this condition, including the use of oral antihistamines, and, in severe cases, using an anti-IgE biologic called omalizumab ( Xolair).

Allergists usually also recommend using thick barrier creams to protect their skin.

Researchers continue to study  Aquagenic urticaria to better understand and develop additional treatments. People with this allergy need extra precautions to avoid discomfort and irritation.

Other Rare Allergies

While allergic reactions to water allergy is one of the rarest, there are many other unusual allergies that affect people. Let’s take a look at some of them:

Sun Allergy (Photosensitivity)

Sun allergy, or photosensitivity, happens when a person’s skin reacts in an unusual way to sunlight. It can cause rashes, itching, or even painful burns after just a little sun exposure [*].

The most common type of sun allergy is called polymorphous light eruption (PMLE). A more serious type, solar urticaria, can cause hives within minutes of being in the sun.

PMLE affects about 10-20% of people, especially those with fair skin. Solar urticaria is much rarer, with only a few cases per million people.

Symptoms of sun allergy include red, itchy rashes, blisters, burning, and swelling. These usually appear on parts of the body that get the most sun, like the face, neck, and arms.

Some people are born with a higher chance of having a sun allergy, while others develop it because of immune system problems. Certain medicines or skin products can also make the skin extra sensitive to sunlight.

To manage sun allergies, people can stay out of the sun, wear protective clothing, and use strong sunscreens. Doctors may also recommend oral antihistamines or oral/topical corticosteroids for relief.

Cold Allergy (Cold Urticaria)

Cold allergy, also called cold urticaria, is a rare condition where a person's skin reacts badly to cold temperatures. When exposed to cold air, water, or objects, they may develop itchy hives, redness, and swelling [*].

In severe cases, cold exposure can cause a dangerous allergic reaction called anaphylaxis, which may lead to trouble breathing, low blood pressure, or even fainting.

This condition affects about 0.05% of people, but it can be hard to diagnose and manage because symptoms vary from person to person. Doctors aren’t sure exactly what causes it, but it may happen because certain immune cells (mast cells) overreact and release histamine when exposed to cold or severe temperature changes (going quickly from really hot to really cold or from really cold to really hot conditions).

Symptoms usually show up within minutes and may include:

• Itchy hives (red, raised, and swollen areas on the skin)
• Swelling (especially on the hands, feet, and lips)
• A burning or tingling feeling on the skin

There  are treatments that can help manage symptoms. Oral antihistamines are often used to reduce reactions. People with severe cases may need to avoid cold exposure and carry an epinephrine auto-injector in case of a serious reaction. In severe cases, using an anti-IgE biologic called omalizumab (Xolair) may be helpful for some patients.

Sweat Allergy (Cholinergic Urticaria)

Sweat allergy, also called Cholinergic Urticaria, is a rare condition where a person’s body reacts to their own sweat [*].

This happens when body temperature rises due to exercise, hot showers, stress, spicy foods, or strong emotions. When this happens, small, itchy hives appear, usually on the upper body, arms, and face.

Experts believe this condition happens because the immune system overreacts to a natural chemical called acetylcholine, which helps the body sweat. This causes histamine to be released, leading to itching, redness, and a burning feeling on the skin.

Symptoms appear within minutes of sweating and can last 30 minutes to a few hours. In rare cases, it can cause swelling, dizziness, or a dangerous allergic reaction (anaphylaxis).

Treatment usually includes oral antihistamines to help with itching and swelling. People with this condition may also try to stay cool and avoid things that make them sweat too much. In severe cases, using an anti-IgE biologic called omalizumab (Xolair) again may be helpful for some patients.

Food-Dependent Exercise-Induced Anaphylaxis

Food-dependent exercise-induced anaphylaxis (FDEIA) is a rare but serious allergic reaction that occurs only when a person eats a specific food and then exercises.

The food alone or exercise alone does not trigger symptoms, but together, they cause anaphylaxis — a severe, potentially life-threatening allergic reaction.

The severity of symptoms can vary from mild (such as hives or itching) to severe (such as difficulty breathing or anaphylactic shock). However, fatal cases are rare. The estimated death rate is 1 in every 1,000 cases of FDEIA [*]

FDEIA can start at different ages. Some people develop it as kids or teenagers, but it most often begins in adults.

The most common foods that cause FDEIA are wheat and shellfish (like shrimp and crab).

Any type of exercise — from hard workouts to regular activities — can trigger symptoms. However, the harder someone exercises, the higher the chance of a reaction.

If someone has a severe allergic reaction (anaphylaxis) during exercise, they need immediate medical help:

• Give an epinephrine shot (EpiPen) right away. If needed, a second dose can be given after 5–15 minutes.
• Lay the person down to help blood flow.
• Give oxygen and fluids through an IV if necessary.
• Start CPR if they stop breathing.
• Doctors may give other medicines like antihistamines or steroids.

To prevent future reactions, all individuals should be referred to an allergist for an evaluation. Also, individuals with FDEIA should avoid eating trigger foods for 4–6 hours before and 1–4 hours after exercise as well as carry epinephrine with them at all times. For those with severe reactions, completely avoiding the food may be the safest option.

Human Touch Allergy (Dermatographic Urticaria)

Human touch allergy, also called Dermatographic Urticaria or Dermatographism, is a condition where even light scratching, rubbing, or touching the skin can cause red, raised bumps or hives. People with this condition can even "write" on their skin using a fingernail, and the marks will appear as itchy, swollen lines.

This condition affects about 2-5% of people, usually starting in the teenage years or early adulthood [*]. Doctors believe that this happens when the allergy cells in the system overreact to intense pressure from scratching or rubbing. This makes the skin release histamine. It can be triggered by things like tight clothing, heat, stress, infections, or temperature changes.

Symptoms appear within minutes after the skin is touched and can last from a few minutes to several hours. The skin may become red, itchy, and swollen.

A doctor may prescribe antihistamines to help with itching and avoiding things that make symptoms worse. Using gentle skincare products can also help keep the skin calm.

Meat Allergy (Alpha-Gal Syndrome)

Meat allergy, also called Alpha-Gal Syndrome, is a rare but serious allergy to red meat and some animal products. Unlike most food allergies, this one takes several hours to show up after eating beef, pork, lamb, or other meats from mammals [*].

This allergy happens because of a sugar called alpha-gal, which is found in these meats. Lone star ticks (Amblyomma americanum) get alpha-gal by ingesting it from the blood of the mammals they bite, such as deer, mice, and dogs. The ticks then pass the alpha-gal on to humans when they bite.

After that, the immune system thinks alpha-gal is dangerous and causes an allergic reaction when the person eats red meat.

Symptoms can be mild or serious and may include itching, hives, swelling, stomach pain, nausea, trouble breathing, or even a dangerous reaction called anaphylaxis.

To stay safe, people with this allergy should avoid red meat and, in some cases, other animal products like gelatin or dairy. Doctors may also give oral antihistamines to help with itching and swelling and prescribe an EpiPen in case of severe systemic reactions. 

Nickel Allergy

Nickel allergy is a common contact skin reaction to nickel, a type of metal found in many everyday items. It is one of the most common metal allergies, affecting about 8-10% of people, with women being more affected than men [*].

This allergy happens when the immune system mistakenly thinks nickel is harmful and causes inflammation in the areas exposed to nickel (swelling and irritation). Touching nickel often or for a long time can make someone more likely to develop the allergy. 

Symptoms usually show up a few hours or days after touching nickel and can include:

• Itchy, red, and swollen skin
• Blisters and dry patches
• Cracked or scaly skin (in severe cases)

To manage this allergy, people should avoid nickel, use barrier creams, and take antihistamines or corticosteroids to help with itching and swelling. If the allergy keeps coming back, a doctor might do a patch test to confirm the allergy and recommend nickel-free products.

The Bottom Line

Allergies vary widely, from common culprits like pollen and pet dander to rare triggers such as water or even exercise.

For those with seasonal or year-round allergies, relief is possible with the right treatment. Allermi’s combination nasal spray is designed to help with congestion, sneezing, runny nose, and inflammation. It offers custom combinations of up to four active ingredients. This includes a decongestant, an antihistamine, an anticholinergic, and a steroid.

Rare allergies require special care, but seasonal and year-round allergy relief is easier with targeted treatments like Allermi.

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