How much damage is caused by smoking 2-3 cigarettes per day on a healthy body?

Drugs have the property of "tolerance." Nicotine is no exception. It is "Progressive diminution of the susceptibility . . . to the effects of a drug, resulting from its continued administration." That means the expected effects of the drug seem to become weaker with use and more is needed to achieve the accustomed effect.

Nicotine's tolerance is slow compared to other drugs such as heroin with tolerance occurring over the course of a few days or weeks. Nicotine takes months or years.

To answer your question, the greatest harm from a few cigarettes a day is that you will find yourself needing more in the near future in order for the experience of those few now. With nicotine it's very gradual, almost unnoticeable but relentless. You may try to limit yourself to those few, but you will find that extremely difficult if not impossible.

There are plenty of reasons not to smoke. This is just one of many. No one plans to become a heavy smoker but it happens. The habitual heavy smoker not only has the worry of serious harm to one's health but also the enormous expense, the difficulty because of smoking bans of finding a place to smoke, and isolation resulting from social disapproval.

What reasons would lead you to end a long term friendship?

I don't care much for friendships at my age (early 20's). I've left so many long lasted friendships in my life that I don't even shrug.I can tell you right off the bat that I left a friendship with my best friend, and pretty

If time - travel will be a thing in future, why havent we still come across people, travelling to the past (today) from the future?

your question contradicts itself "IF time travel were possible" 'IF' is the keyword and even if we assume it does become possible maybe we can't travel to the past or maybe time travelling is not available for the public and is only for scientific research and as we have many written records of our current time

Are chemical engineers in demand?

No,I have edited the answer to since experienced chemical engineers will be in demand. But have assumed you are talking about new graduates, in that case you may as well do a degree in psychology or whatever mickey mouse course your country does.Don't believe the lies. Many countries churn out chemical engineers and