New Delhi: The Centre has written to all states and union territories warning against the use of N-95 masks with valved respirator by people, saying these don't prevent the virus from spreading out and are "detrimental" to the measures adopted for its containment.

The Director-General of Health Services in the Ministry of Health, in a letter to the Principal Secretaries of health and medical education of states, said it has been observed that there is "inappropriate use" of N-95 masks, particularly those with a valved respirator, by the public other than designated health workers.