In 2000, the American Academy of Dermatology warned Americans: eczema was on the rise. In the warning, the group of dermatologists said that the rate of atopic dermatitis — an inflammatory skin condition also known as eczema — had nearly tripled since 1970. At the time, it was estimated that nearly 6 percent of all Americans had the condition that can cause itchy, red, and scaly skin. Today, the National Eczema Foundation estimates that at least 10 percent of Americans have eczema, and that one in ten people will have eczema in their lifetime.
Despite the increase in prevalence, which has been documented by many researchers — especially among children— one aspect from the warning that donned headlines 23 years ago remains the same: nobody knows what's causing an increase in the number of people diagnosed with the itchy-skin condition.
"We need to learn more."
Dr. Ross Radusky, a board-certified dermatologist at the Dermatology Treatment and Research Center in Dallas told Salon that "one possibility is that as our population increases and people live in more densely populated locations, the rates of eczema will naturally rise, [but] more research is definitely needed."
As one study found, around the world the prevalence of eczema increased only 0.98 percent over the last decade in adolescents, and 1.21 percent in children. However, there were major variations based on regions as the rise in eczema was most pronounced in urban areas. While there is no definitive reason as to why that is, as Radusky said, there is an increasing suspicion that pollution could be to blame.
"Past studies have looked at the rates of eczema in urban versus rural settings, and the incidence rates tend to be higher in city settings, places you'd expect higher pollution rates," Radusky said. "There are other factors in that equation, but it is important to know that pollutants affect rates of asthma, seasonal allergies, and possibly even food allergies, and all three have been linked with higher rates of eczema."
"Allergies are worse here in general due to air pollution, climate change, industrialization and disruption in our microbiomes from overexposure to chemicals, pesticides, processed foods, plastics."
Radusky said by their nature, pollutants are foreign substances that shouldn't be in our daily lives, and our skin might not appreciate that.
"Our skin doesn't like intruders," Radusky said. "It needs to mount a significant defense and when it does that and forms a high inflammatory state, an eczema flare may not be far behind."
In March, dermatologists said they observed an increase in patient visits to dermatologists for eczema during the California wildfires. In a study published in the journal Science Advances in January, researchers found a link between common chemicals and eczema. Specifically, by testing on mice, the researchers found that when the skin was exposed to isocyanic acid — a component of wildfires, cigarette smoke, and car exhaust from catalytic converters — the bacteria that normally live on skin stops producing oils that the skin needs to stay healthy, leaving the skin vulnerable to a flare-up.
Part of not knowing what's behind the rise in eczema stems from the complexities of eczema itself. Scientists know that eczema happens when a person's immune system has an overreaction to an irritant or trigger. The immune system sees a trigger as an invader, like a virus or bacteria, and as a result the body's immune system creates inflammation. The inflammation causes the physical symptoms of eczema on a person's skin. However, despite functioning similarly to an autoimmune disease, eczema is not classified as one. That's because the reaction doesn't technically result in the body attacking its own healthy cells or organs.
Radusky said it is largely believed that there is a genetic component to eczema, specifically a deficiency in a protein called filaggrin.
"That protein helps keep the cells that make our skin stay glued together. Without it, the tiny holes that exist between our skin cells allow water to escape and that causes a very inflammatory and itchy skin condition known as eczema," Radusky said. "We think of eczema as a mix of environmental and genetic factors. Certain stressors like dry, cold climates as well as seasonal and food allergies can set off the inflammatory cascade that leads to the rash we know as eczema."
But it's the "interplay" between genetics and environmental causes that are difficult for researchers to suss out an exact cause behind the rise.
"While we know the leading cause of atopic dermatitis (the most common form of eczema) is the protein deficiency filaggrin, it is not the only reason we see flares," Radusky said.
Dr. Purvi Parikh, an allergist with the Allergy & Asthma Network, told Salon via email that she believes eczema could be more common in the U.S. due to environmental factors, like pollution.
"Allergies are worse here in general due to air pollution, climate change, industrialization and disruption in our microbiomes from overexposure to chemicals, pesticides, processed foods, plastics," Parikh said. "Pollutants make you more allergic in general and this can trigger eczema, being an allergic individual predisposes you to developing eczema compared with a non-allergic person."
Indeed, Radusky said food allergies, seasonal allergies and eczema form what is known as the "atopic triad."
"They run together and it is known that the inflammatory reaction that occurs in all these conditions follow the same pathway," he said. "Our immune system reacts very much the same to both eczema triggers and asthma/allergy triggers."
Unfortunately, there is no cure for eczema. However, there are many treatments available. And while other conditions like celiac disease, which are on the rise for unknown reasons, are hard to understand due to a lack of funding, Radusky said that's not the case with eczema.
"I don't think a lack of funding is the reason why it is difficult to know what causes eczema. There has been tons of research and new medications that limit the body's inflammatory response common eczema triggers," Radusky said. "So while we can't cure eczema at the current time, we have new therapies that can limit how bad a flare can be."
CORRECTION: An earlier version of this story incorrectly identified isocyanate as causing the issue with dermal bacteria, when it is technically isocyanic acid, a compound in the functional group isocyanate. The story has been updated.
