To mask or not to mask? For a while, it really wasn’t a question, as stores, coffee shops, and even hiking trails required protective face covering to prevent the spread of Covvid-19. But now that some locations and situations make mask-wearing a little less than mandatory, you may be wondering: When should I wear one, and do they work? And could wearing a mask for too long be dangerous?
The conversation began in February, when widespread shortages of N95 respirators and surgical masks for healthcare workers were recognized. That broad gap between supply and demand initially raised questions about who needs masks, and whether they’re even the most effective way to prevent the spread of Covid-19.
The Centers for Disease Control (CDC) initially emphasized that washing your hands frequently and avoiding touching your face—especially your eyes, nose and mouth—with unwashed hands was one of the most important actions you could take. The World Health Organization (WHO) further noted that wearing masks can create a false sense of security, leading people to neglect important preventive measures like hand hygiene, physical distancing and avoiding touching your face. U.S. Surgeon General Jerome Adams, MD, also notes that wearing a mask improperly can increase your risk of infection; if you’re not used to wearing one, it’s likely you’ll touch your face more frequently—especially if a mask doesn’t fit right and you’re constantly adjusting it. Additionally, cloth masks don’t protect you from respiratory droplets that carry a virus; they’re too loose, have no air filter and leave the eyes exposed.
Now, as we know more about Covid-19, mask-wearing recommendations focus on the idea of protecting others from cough or sneeze droplets, if you yourself have the virus—especially important if you’re asymptomatic or pre-symptomatic. But some masks actually make the problem worse; those with exhalation valves that make it easier to breathe allow potentially infected droplets to escape, increasing the risk to others if you’re infected. The problem is, many public venues that require face coverings don’t distinguish between the two.
The prevalence of masks has led to questions about the safety of wearing them for extended periods of time. You’ve certainly read the internet buzz around hypoxia—a condition in which the body is deprived of adequate oxygen—and cognitive impairment. There’s no real evidence that wearing masks poses a significant danger for most people, but some organizations question the safety of extended mask-wearing for people with chronic asthma, chronic obstructive pulmonary disease (COPD), or other lung-related diseases. Wearing a mask can make it harder to draw air into the lungs, triggering asthma for some people; it can also cause anxiety, which changes breathing patterns.
The problem is, the coronavirus is so new, few if any studies have examined the effects of the general public wearing face coverings ranging from surgical masks to cotton bandanas for extended periods of time. Several studies of N95 masks use in healthcare workers note increased headaches, thought to be caused in part by straps and pressure from the mask, in part by a reduction in blood oxygenation or an elevation in blood C02. One study found 81 of health care workers developed headaches from wearing an N95 mask. Another study of health care workers found surgical masks lead to a significant reductions in blood oxygen as well. And some doctors suggest wearing a mask poses often serious risks. Russell Blaylock, MD, a board-certified neurosurgeon, links extended mask use with significant health problems, including headaches, increased airway resistance, carbon dioxide accumulation, hypoxia, diminished immune function, and impacts on cardiovascular health. , , , , , 
In general, according to the CDC, anyone with a confirmed or suspected infection should wear surgical masks; healthcare workers should wear N95 respirator masks and goggles, and anyone going out in public should wear some kind of protective face covering. Who shouldn’t wear a mask: children under the age of two, anyone who has trouble breathing, and anyone who’s unconscious or can’t remove a mask without help. If you have exercise-induced asthma, some health officials say you should still wear a mask, unless you’re on a trail or other area where you won’t come in contact with others. Or if you have a condition that limits your ability to breath, carry a bandana with you, and cover your face when you’re in a public setting.
4 Do’s and Don’ts for Wearing a Face Mask
Here’s how to prevent an increased risk of infecting yourself when you’re wearing the mask:
1. Don’t touch your face; if you do, wash or sanitize your hands.
2. If you have to adjust your mask, take it off, fold it so the outer surface folds against itself, wash your hands thoroughly, and then put it back on.
3. Masks should ideally be washed after every single use and dried on high heat. If your mask is heavily soiled or damaged, toss it.
4. If you’re wearing a mask to protect others from infection, it should be snug against the sides of your face, secured with ties or ear loops, made with multiple layers of material and should not have an opening or exhalation valve. It should fit well, so you’re not constantly adjusting it, and should allow you to breathe without restriction to minimize any potential health impacts.
 Zhu JH et al. Effects of long-duration wearing of N95 respirator and surgical facemask: a pilot study. J Lung Pulm Resp Res 2014:4:97-100.
 Ong JJY et al. Headaches associated with personal protective equipment- A cross-sectional study among frontline healthcare workers during COVID-19. Headache 2020;60(5):864-877.
 Bader A et al. Preliminary report on surgical mask induced deoxygenation during major surgery. Neurocirugia 2008;19:12-126.
 Shehade H et al. Cutting edge: Hypoxia-Inducible Factor-1 negatively regulates Th1 function. J Immunol 2015;195:1372-1376.
 Westendorf AM et al. Hypoxia enhances immunosuppression by inhibiting CD4+ effector T cell function and promoting Treg activity. Cell Physiol Biochem 2017;41:1271-84.
 Sceneay J et al. Hypoxia-driven immunosuppression contributes to the pre-metastatic niche. Oncoimmunology 2013;2:1 e22355.