Wearing a mask, even an improvised one, is better than no mask.

A P100 respirator is better than a N95 mask, which is better than a surgical mask, which is better than a scarf or pillowcase, which is better than nothing. Don’t despair if you don’t have the best mask. Make do with what you have. Try to get it to fit as well as possible.

In addition to some degree of protection against inhaling droplets with virus in them (or exhaling onto others if you’re sick), masks will prevent you from touching the mucous membranes of your face with dirty hands when you’re out in public.

Numerous studies show that masks can cut down on influenza transmission. [0] Nearly every Asian public health ministry recommends that people wear masks in public, especially during the winter flu season. Hong Kong, Singapore, South Korea, and Taiwan all recommend wearing masks, and all of these countries have been effective in slowing the spread of COVID-19 within their borders.

Since mask supply is limited, there are questions about mask reuse. There are conflicting reports about whether it is safe to sterilize and reuse masks. [1] [4] Almost everyone recommends discarding masks once used in a high-risk setting (eg a hospital, or contact with a person with COVID-19). However, reuse after low-risk use may be possible. Some sources claim that improvised fabric or surgical masks can be sterilized in boiling water and then dried, disinfected with UVC light, or left out in the sunlight for several days. [0] [1] N95 masks need to stay dry. An old study from SARS-CoV suggests that temperatures of 60C / 140F for 30 minutes will destroy a different coronavirus. [2] There is no analogous study for this coronavirus yet, but it’s likely its temperature tolerance is similar. N95 masks appear to only mildly be damaged by this level of heat. [3] Thus, it’s possible you could “bake” your used N95 masks at low heat in the oven (eg 180F) to sterilize them without damaging them. I’ve tested this on the 3M brand N95 masks we have and it appears to work.

Thinking systemically, it’s true that healthcare workers have the greatest need for masks as they have the greatest exposure. However, that doesn’t mean you shouldn’t take whatever you already have and make use of it. Contrary to what the CDC is saying, masks do help prevent the spread of influenza, and there’s ample research to support it.

If you do have extra masks you're not using and they're still sealed in their original packaging, please consider donating them to a local hospital where they'll do a lot of good by keeping healthcare workers healthy.

I believe the CDC is trying to cover for the fact that they did not adequately stockpile masks for a pandemic, and now they don’t have enough for healthcare workers. They could have said “Hey, we messed up big time, and we need you all to make a small personal sacrifice so that the people who are putting their lives on the line are adequately protected. We’re going to make sure this never happens again.” But instead they’re saying “The Centers for Disease Control and prevention does not recommend that well people wear a face mask to protect themselves from respiratory illnesses, including COVID-19”.

This goes without saying, but wearing a mask alone won’t protect you. You should be regularly washing/sanitizing your hands and avoiding crowds if at all possible.

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Sources :

The case for masks
[0] https://www.inkstonenews.com/health/coronavirus-health-researchers-urge-global-authorities-consider-broadening-use-face-masks/article/3074453

Washing surgical masks:
[1] https://focustaiwan.tw/society/202002020012

Heat for inactivation of the original SARS coronavirus:
[2] https://www.ncbi.nlm.nih.gov/pubmed/15118911

Mask safety during sanitization
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781738/

Claims of mask steaming as ineffective:
[4] https://factcheck.afp.com/novel-coronavirus-health-experts-warn-against-steaming-face-masks-reuse-after-misinformation-chinese

Homemade masks: https://www.researchgate.net/publication/258525804_Testing_the_Efficacy_of_Homemade_Masks_Would_They_Protect_in_an_Influenza_Pandemic
https://academic.oup.com/annweh/article/54/7/789/202744

Surgical masks and N95 masks:
https://www.ncbi.nlm.nih.gov/pubmed/23498357
https://www.ncbi.nlm.nih.gov/pubmed/20095070
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3306645/ (interesting experimental setup)

Home wearing of masks to prevent family members infecting one another:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2662657/

Good Reddit discussion:
https://www.reddit.com/r/Coronavirus/comments/fgorv3/no_need_to_wear_a_mask_experts_urge_health/fk5xppo/