New research from German academics suggests that face masks may increase the risk of stillbirths, testicular dysfunction, and cognitive decline in children. The review of dozens of studies on face coverings found that masks can cause mild carbon dioxide poisoning when worn for long periods.

The researchers believe that masks create a pocket of dead space between the mouth and mask, which traps toxic gas, including carbon dioxide. They point out that the buildup of CO2 in pregnant women’s bodies could cause complications for the unborn fetus and contribute to oxidative stress, affecting cognition and causing testicular issues in men. The findings were published in the journal Heliyon.

The study has raised concerns, but independent doctors have questioned the conclusions. The German researchers did not directly look at health complications and mask use and described the link as “unlikely”. However, the researchers found that animal studies showed exposure to CO2 at similar levels to those found behind masks led to stillbirths and birth defects, irreversible neuron damage, and testicular cell destruction.

The researchers gathered data from 43 previously published studies on exposure to CO2, mask-wearing, and pregnancy. After wearing a mask for more than five minutes, CO2 levels in the inhaled air rose to between 1.4% and 3.2%, according to their findings. Masks provide breathing resistance and create a dead space that traps CO2, leading to more inhaled and re-breathed CO2, the reviewers said.

The main caveat of the research is that the studies looking at the potential toxic effects of carbon dioxide are animal studies – because these experiments would not be ethical in humans. The researchers also noted that none of the studies in their review looked directly at mask use and miscarriages, infertility, and neurodevelopment disorders.

The debate about the effectiveness of masks has been ongoing for three years. The biggest review by the Cochrane Institute, based in London, found they made little to no difference to infections, but smaller studies suggest there is a lower risk of catching Covid. Mask mandates on transportation systems in America were backed by penalties of up to $3,000 for repeat offenders.

It’s essential to note that factors other than mask-wearing are likely to be at play when it comes to pregnancy complications and stillbirths, such as hospital closures and delayed care.