A recent Stanford study released by the NCBI, which is under the National Institutes of Health, showed that masks do absolutely nothing to help prevent the spread of COVID-19 and their use is even harmful.
NIH published a medical hypothesis by Dr. Baruch Vainshelboim (Cardiology Division, Veterans Affairs Palo Alto Health Care System/Stanford University, Palo Alto, CA, United States).
The study concludes (emphasis added):
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 proper and scientific evidence-based approach with respect to wearing facemasks, when the latter is considered as preventive intervention for public health.