Here's a study from Stanford university, published on the National Center for Biotechnological Information website, It concludes that masks are
"ineffective to block viral particles" and "prolonged and continues (sic) effect of wearing facemask is maladaptive and could be detrimental for health."
It's a matter of size.
According to the current knowledge, the virus SARS-CoV-2 has a diameter of 60 nm to 140 nm [nanometers (billionth of a meter)] [16], [17], while medical and non-medical facemasks? thread diameter ranges from 55 ?m to 440 ?m [micrometers (one millionth of a meter), which is more than 1000 times larger [25]. Due to the difference in sizes between SARS-CoV-2 diameter and facemasks thread diameter (the virus is 1000 times smaller), SARS-CoV-2 can easily pass through any facemask.
Link
Conclusion
The existing scientific evidences challenge the safety and efficacy of wearing facemask as preventive intervention for COVID-19. The data suggest that both medical and non-medical facemasks are ineffective to block human-to-human transmission of viral and infectious disease such SARS-CoV-2 and COVID-19, supporting against the usage of facemasks. Wearing facemasks has been demonstrated to have substantial adverse physiological and psychological effects. These include hypoxia, hypercapnia, shortness of breath, increased acidity and toxicity, activation of fear and stress response, rise in stress hormones, immunosuppression, fatigue, headaches, decline in cognitive performance, predisposition for viral and infectious illnesses, chronic stress, anxiety and depression. Long-term consequences of wearing facemask can cause health deterioration, developing and progression of chronic diseases and premature death. Governments, policy makers and health organizations should utilize prosper and scientific evidence-based approach with respect to wearing facemasks, when the latter is considered as preventive intervention for public health.
Table 1
Physiological and Psychological Effects of Wearing Facemask and Their Potential Health Consequences.
Physiological Effects
? Hypoxemia
? Hypercapnia
? Shortness of breath
? Increase lactate concentration
? Decline in pH levels
? Acidosis
? Toxicity
? Inflammation
? Self-contamination
? Increase in stress hormones level (adrenaline, noradrenaline and cortisol)
? Increased muscle tension
? Immunosuppression
Psychological Effect
? Activation of ?fight or flight? stress response
? Chronic stress condition
? Fear
? Mood disturbances
? Insomnia
? Fatigue
? Compromised cognitive performance
Health Consequences
? Increased predisposition for viral and infection illnesses
? Headaches
? Anxiety
? Depression
? Hypertension
? Cardiovascular disease
? Cancer
? Diabetes
? Alzheimer disease
? Exacerbation of existing conditions and diseases
? Accelerated aging process
? Health deterioration
? Premature mortality