To maintain hygiene you should wash your face 2 times daily which includes once in the morning and once again at night.
Washing your face twice a day helps remove any oil, makeup and dirt that can accumulate on the face during the day and night.
You should also wash your face after you sweat.
Or if you work in dirty environments it can be a good idea to wash your face more often if needed.
As long as you're washing your face at least twice a day you're doing good to keep your face clean and your skin healthy.
If you need to wash your face more often you can also just rinse the face with some water instead of using soap or cleanser.
Just avoid over washing your face.
over washing your face can cause the skin to become red and inflamed and could also lead to inflammatory rashes, perioral dermatitis or even acne breakouts.
You could also cause your skin to become rough to the touch or even very oily or yet dry and flakey.
If you don't wash your face often enough, the oil and the old dead skin cells will combine with dust from the air and then coat the face with dirty grime.
The dirty grimy layer will then eventually clog your skins pores and as a result you could get pimples or even boils on your face.
You will also probably feel bad, like it does after you work outside on a hot dusty day.