I researched the effectiveness of the standard blue NHS masks and this is what I found:
Source Control: They are very effective at reducing the distance and intensity of air, moisture, and droplets released when coughing, sneezing, or talking.
Protection Level: They provide a physical barrier to large droplets and splashes, protecting the wearer from direct contamination to the mouth and nose.
Limitations: Because they do not fit tightly to the face, they allow for leakage around the sides, meaning they are less effective at filtering out very fine, airborne particles.
Clinical Evidence: A 2024 review found that when worn consistently and correctly, masks and respirators reduce the transmission of respiratory infections like COVID-19.