Mutyambai observed in the letter that disregard for the dress code was a violation of Chapter 31 under the Service Standing Orders (SSO), which guide the operations of the National Police Service.
Notably, Mutyambai cautioned officers against uploading videos on social media while drunk, dancing or uttering obscene words while in uniform.
Several officers have gone viral in recent months for different reasons. Videos of dancing and singing police officers are common, while others gained infamy with viral videos that showed them behaving badly while on duty.
In one video that was shared by, among others, Deputy President William Ruto, two officers were seen fighting over a bribe from a charcoal trader.
In another, a drunk officer was seen being helped by members of the public after falling into a ditch while in uniform. Several officers have also gone viral during various operations when they were captured clobbering citizens.
In the most recent instance, Mlango Kubwa MCA Patricia Mutheu was a victim as she was assaulted by police at City Hall, Nairobi.
Mutyambai advised officers to observe high etiquette in their use of social media platforms.
In his letter, Mutyambai also cautioned against mixing of police uniform with civilian clothing.
â€œPolice uniforms should not be worn with any visible article of civilian clothing, articles or anything that is not police uniform. Mixing of uniform will not be allowed,â€ he asserted.
The IG further claimed that the disregard for the police dress code had contributed to moral deterioration within the police service. His letter came against the backdrop of activists demanding action over a surge in reported cases of police brutality and extra-judicial killings.
He went on to remind male and female officers on regulations on hair and make-up, particularly when they were in uniform.
â€œMake-ups should be discreet and only natural and clear nail polish may be used. Male officers will always have short and well-kept hair,” the letter read in part.
In the letter copied to various command stations, bosses were directed to ensure their juniors to comply with the directives.