The cleanest part of the human body is the blood, cerebrospinal fluid and internal organs which are strictly internal areas isolated from the outside of the body.
Even the internal organs like the heart, the brain and the liver are also other cleanest parts of the human body.
The cleanest exposed external parts of the human body include the eyes, "most specifically the cornea" is considered the cleanest part of the human body on the outside due to tears that contain antibacterial enzymes that also continuously wash away microbes.
Our human bodies are also an ecosystem of trillions of microbes, so when we define "clean" it depends on whether we mean the free of germs (sterile) or self cleansing.
Among parts of our human body's that are exposed to the outside, our eyes are often considered the cleanest external parts of the body.
Our eyes have self cleaning mechanisms, as blinking constantly also cleans our eyes with tears, which also contain antibacterial enzymes like lysozymes that kill bacteria and wash away debris.
The cleanest parts of our human body's when it comes to the internal sterile sites are the internal environments that are completely free of microorganisms.
These internal sterile sites of the human body, like the heart, brain and kidneys as well as our fluids like cerebrospinal fluid and blood are the cleanest.
And if these areas of the human body host any bacteria, it often indicates a serious infection.
The skin can also be pretty clean as long as we bathe or shower often enough.