Eczema, also known as atopic dermatitis, is a skin disease that's chronic and inflammatory -- meaning it involves an immune system reaction. It affects 18 million adults (more than 7%) and 9.6 million children (13%) in the United States, according to the researchers from University of Southern California Keck School of Medicine.
They analyzed 15 previous studies that included 310,681 eczema patients and about 4.4 million patients without eczema. Study locations were in North America, Asia, Europe and Africa.
The researchers found that patients with eczema were 44% more likely to have suicidal thoughts and 36% more likely to attempt suicide compared to people without the skin condition. However, due to incomplete data or inconsistent results, the researchers did not find a difference in the risk of completed suicide between eczema patients and others.
So what explains the higher rate of self-destructive thoughts and actions?
The study authors explain that eczema is associated with an increase in proinflammatory cytokines, a type of immune system molecule found at high levels wherever there is an infection. Higher levels of proinflammatory cytokines in the central nervous system may disrupt the balance of neurotransmitters in the brain and lead to negative thoughts, they theorized.
Dr. Joel M. Gelfand,
a professor of dermatology and of epidemiology and medical director of the Dermatology Clinical Studies Unit at the University of Pennsylvania Perelman School of Medicine, told CNN the possibility of cytokines disrupting brain chemistry is only "a theory."
"The causal role of inflammation and suicidal activity and outcomes is not established yet," said Gelfand who was not involved in the analysis. Still, he believes the new research is "important."
"The country is facing an epidemic in suicide, it's really a public health crisis, and the more we can understand what conditions and behaviors lead to suicidal thinking, behavior and actions, the more we can figure out ways to identify people at risk and hopefully prevent these really terrible outcomes for people," Gelfand said.
Suicide and suicidal behavior are "challenging to study -- sometimes they are statistically rare so pooling a number of studies to get better insight is appropriate scientifically," noted Gelfand, who was not involved in the new study. "The study reminds us that there is clearly an association here but there is a lot more we need to figure out."
Dr. Eric Simpson
, a professor of dermatology at Oregon Health & Science University's School of Medicine, told CNN in an email that the new research is "consistent" with previous studies which "demonstrate a strong association, in children and adults, between having atopic dermatitis (eczema) and mental health conditions such as anxiety and depression."
He agrees with Gelfand that the cause of this connection between eczema and mental health conditions is not yet known. It might be explained by the negative impacts of a chronic disease, poor sleep due to the itch, or even "the effect of inflammation on the developing brain," said Simpson, who was not involved in the new analysis. "Shared genetic risk factors could be another explanation," he said.
Eczema, a 'serious chronic disease'
"Atopic dermatitis is not 'just eczema,' but is a serious chronic disease that can greatly impact a person's entire life," he said, adding that mental health specialists could help patients manage depression and help "care for the whole patient."
Last year, an eczema patient in Hong Kong
killed herself and her parents, police said. At the time, Hong Kong police suggested her skin condition might have motivated the attack. But that case does not "fairly illustrate" the role played by eczema in mental health, said Simpson. "This patient appeared to be a deeply troubled person in many ways," said Simpson, who did not treat the patient in the Hong Kong case.
Gelfand's message for people living with eczema and their families, friends and health care providers is awareness.
"They face a lot of discomfort in their skin, a lot of sleep disturbance from their disease, a lot of social isolation and stigma, so being supportive of people suffering with eczema is really important," he said.
Still, there is hope, said Gelfand: "Therapies are rapidly evolving and there's a lot of new ways to help people with this disease."