If I have no pressing need (i.e. outing, doctor's appointment, job, heavy sweating or dirty work) I can go anywhere between only 2 to 3 times per week, washing my hair even less. What I might do on the "off days" are washcloth baths.

If I am in a severe bipolar episode, I have been known to shower less than once per week or even twice per month. Again, my hair usually got washed even less frequently.