I heard from someone today that people can be allergic to water. Is this true? Do we know why?
-A curious adult from California
December 4, 2015
As strange and impossible as that seems, the answer is YES! Some people have an allergic reaction to water. This is called “aquagenic urticaria.”
These poor people often get red, swollen marks all over their bodies (except the palms of their hands and soles of their feet), and most also feel itchy. Some can even feel lightheaded, nauseous or have trouble breathing after touching it. Just from water!
And sometimes, like lots of other allergies, this can run in the family. This tells us that genetics probably plays a role.
But surely people can’t be allergic to plain old water. It must be something else.
Doctors once thought the same thing. They thought they must be allergic to something in the water.
That’s because tap water isn’t pure water. It has other minerals like chlorine to keep it free of bacteria and fluorine to keep our teeth healthy. So doctors thought people must be allergic to one of these things.
To see if this was true, doctors did a few tests every time someone came in with signs of a water allergy. First, they soaked a towel in tap water (that has minerals in it) and put it on the person’s skin for 10 minutes. They then looked for any red spots and asked the person how they were feeling.
Next, the doctors soaked another towel in pure water (with all of the minerals removed) and put it on a different part of the person’s skin for 10 minutes. The doctors looked for red spots again.
It turns out, some people react to just tap water, some react to just pure water, and some react to both. So some people are allergic to plain old water.
But people have to shower, right?! And wash their hands?! And what do these people do if they get caught in the rain?!
About half of these people can deal with their symptoms by taking allergy medicines. These antihistamines are the same thing you can take if you are allergic to other things.
But this only works for about half of people who are allergic to water. The other half can try something else – using UVB light to thicken their skin.
The idea here is to make the skin on the whole body look and act like the skin on the palms of your hands and soles of your feet. This makes it harder for water to get to the skin’s deeper layers. The skin’s deep layers is where doctors think the allergic reaction is happening.
Sometimes, though, nothing works. These people need to keep away from water as much as they can. They might have to, for example, clean themselves with rubbing alcohol instead of showering.
Do these people also have an allergic reaction to water when they drink it?
As far as doctors know, no one is allergic to water when they drink it, just when their skin touches it. And it’s a good thing, because without drinking water, we wouldn’t live very long!
Is this type of water allergy something someone is born with, or is it something they get when they grow up?
The youngest person that we know of who has a water allergy was 18. As far as we know, no babies are allergic to water.
But we don’t know exactly why people develop this allergy. Scientists have a couple of ideas, though.
One way this could happen is that chemicals that cause allergies can “hitch a ride” with water. The body reacts against a chemical but since water is there too, it reacts against the water as well.
So your body’s army, the immune system, attacks the chemicals. The attack is what makes red marks on the skin and causes itchiness.
Along the way it also mistakes water for something bad. Now the person is allergic to water and the chemical!
Does it run in families?
Sometimes more than one person in a family can be allergic to water. This happens because the instructions that tell the immune system how to work are in our genes. And families share a lot of the same genes.
To understand all of this, let’s step back a bit and talk about cells.
Each of us is made up of trillions of cells. We have different types of cells that do different things.
For example, we have heart cells and eye cells and skin cells. These cells know what to do because they all have an instruction manual called DNA.
Each chapter in the instruction manual is called a gene. We have genes for all sorts of things.
We have genes that tell our eyes what color to be and we have genes that tell us how tall we’re going to be. We also have genes that set up our immune systems. Remember, the immune system is the body’s army and attacks dangerous infections and chemicals.
Some people have instructions that make their bodies more likely to think that water might be dangerous. Now their bodies may react to water even though water is perfectly safe!
This same sort of thing happens when people have hay fever. Except that instead of being allergic to water, these people are allergic to pollen.
Like the rest of our genes, these instructions can be passed down from parents to children. So if you get the instructions from your parents that make them more likely to be allergic to water, then you may end up allergic, too.
Scientists think that people with water allergies aren’t born with an immune system that reacts against water. Instead, their immune system is primed to maybe one day turn against good old H2O.
What happens is that something in the environment tricks immune cells so they misunderstand their instructions. Now the immune system starts thinking water is dangerous.
We still don’t know what it is that tricks the body. And we still don’t know exactly how water allergies are passed on. And we might not figure it out any time soon because there aren’t many people with water allergies to study!
By Tia Moscarello, Stanford University