"Wearing a face mask is certainly not an iron-clad guarantee that you won’t get sick – viruses can also transmit through the eyes and tiny viral particles, known as aerosols, can penetrate masks.

However, masks are effective at capturing droplets, which is a main transmission route of coronavirus, and some studies have estimated a roughly fivefold protection versus no barrier alone.

If you are likely to be in close contact with someone infected, a mask cuts the chance of the disease being passed on. If you’re showing symptoms of coronavirus, or have been diagnosed, wearing a mask can also protect others. So masks are crucial for health and social care workers looking after patients and are also recommended for family members who need to care for someone who is ill – ideally both the patient and carer should have a mask."

The Guardian