If you smoke hookah once in a blue moon, is it harmful?

Smoking what?: Very occasional tobacco smoke (or marijuana smoke) is unlikely to cause major harm (unless you drive under influence), but increases the chance that you will ultimately smoke more. In people with lung problems, even occasional use can be a problem.

Hookah: This is like asking - is it harmful to eat rat poison if I only do it once in a blue moon? Per the Mayo Clinic: Per Dr. T Hays- " Hookah smoke contains high levels of toxic compounds, including tar, carbon monoxide, heavy metals & cancer-causing chemicals (carcinogens). In fact, hookah smokers are exposed to more carbon monoxide & smoke than are cigarette smokers." REF: https://www.mayoclinic.o