Is smoking a sin?
I don't think so. the Bible does not mention directly about smoking tobacco cigarettes or cigars.
1 Corinthians 10:
CDC lists many bad health effects:
It is wise not to smoke.
Similarly for vaping, it is not a sin but it is not wise.
See also
Smoke weed.
I think most people are unqualified to answer that question. Let me give some thoughts about that:
A lot of people consider anything addictive to be sinful as it enslaves the person: ie (I will just list the consumed things that can be addictive) alcohol, tobacco, coffee, food, drugs.
Jesus answered appropriately:
Matthew 15:11 Not what goes into the mouth defiles a man; but what comes out of the mouth, this defiles a man.” 12 Then His disciples came and said to Him, “Do You know that the Pharisees were offended when they heard this saying?” 13 But He answered and said, “Every plant which My heavenly Father has not planted will be uprooted. 14 Let them alone. They are blind leaders of the blind. And if the blind leads the blind, both will fall into a ditch.”
So I would follow the teaching in Matthew 15:11-14 in that nothing we take in is a sin, but if it causes us to sin in other ways, like excessive drunkenness and acting foolishly then it can lead to sin. Then it becomes unwise and should be refrained from.
We could seriously debate about whether or not tobacco causes cancer. For instance, it can in certain people lead to cancer, and in others they have and will live a full life and never get cancer. So when they say tobacco increases your risk for cancer, that is probably an incorrect statement to make. As they cannot prove someone will get cancer from tobacco.
It is certainly better to go without tobacco. And the question wasn't asked about alcohol but I see many weighing in on that subject. The bible prescribes alcohol for certain conditions:
Proverbs 31:6 Give strong drink to him who is perishing, And wine to those who are bitter of heart.
It also warns of excessive drunkenness as unwise:
Proverbs 20:1 Wine
is a mocker, Strong drink
is a brawler, And whoever is led astray by it is not wise.