Docs can you explain, is smoking once a month that risky?

Depends on how much: you are smoking. There are some people who can have 1-2 cigarettes on rare occasions, and not progress, but the biggest risk to you is progressing to regular smoking. Any amount of smoke, even that of second-hand smoke, can do harm. It can bring on asthma is susceptible people, increase numbers of respiratory infections and have a measurable increase in cancer risk.