Wearing protective face masks is now a common practice, thanks to the COVID-19 pandemic. But while health officials are busy reminding the public to keep their masks on, researchers are starting to question whether face masks are really effective. Studies have shown that they may not provide the level of protection that mask advocates initially rest their faith on.

Now, more experts are going on record to say that prolonged use of face masks – from cloth masks to N95 respirators – may pose several threats to health. Read the evidence below to learn more about the dangers of face masks and what you can do to prevent them.

Face masks bad for lung health

The American Lung Association stated that prolonged use of face masks like N95 respirators may lead to carbon dioxide build-up in people with a pre-existing lung condition. Excessive levels of carbon dioxide in the body, known as hypercapnia, can cause symptoms such as headaches, dizziness and shortness of breath. While most healthy individuals are not likely to have this issue, anyone with a respiratory illness, such as chronic obstructive pulmonary disease or COPD, may be at risk of the condition.

Dr. Amesh Adalja of the Johns Hopkins Center for Health Security in Maryland also said that N95s are not intended for the general public but for healthcare workers and the patients they care for.

“It’s uncomfortable to wear, and it does restrict your breathing,” Adalja told Health. (Related: Study: N95 masks with exhalation valves cannot stop the spread of coronavirus.)

Unfortunately, even other types of masks can be bad for the lungs. A 2015 study published in the journal BMJ Open shows that the use of cloth masks can increase the risk of respiratory illness and viral infection in a healthcare setting. Researchers found that particle penetration in cloth masks was almost 97 percent. They suspect that moisture retention, reusing the masks and poor filtration may explain the increased risk of infection.

“We should be cautious about cloth mask use in healthcare settings, particularly high-risk situations,” said lead author Raina MacIntyre of the University of New South Wales in Australia.

Oral and skin problems caused by face masks

Experts use the term “mask mouth” in reference to the host of dental and oral health problems caused by the prolonged use of face masks. Dr. Bridget Glazarov, a general and cosmetic dentist in New York City, said that wearing a face mask forces a person to breathe through the mouth. This dries out the saliva and causes dry mouth, Glazarov said.

Dry mouth can lead to cavities, gum disease, bad breath and tooth decay, according to Dr. Jennifer Bell, a North Carolina dentist and spokesperson for the Academy of General Dentistry. The National Institute of Dental and Craniofacial Research also said that persistent dry mouth can increase the risk of oral infections with bacteria like Candida albicans, which is responsible for oral thrush.

“Rebreathing your own expelled air at higher quantities than normal can cause a build-up of bad bacteria,” explained Bell.

Masks can also irritate the skin and cause “maskne.” Also known as acne mechanica, maskne is caused by the combination of heat, friction, skin occlusion and excessive moisture, according to Dr. Harry Dao, a dermatologist at Loma Linda University Health in California.