Smoking in moderation is allowed (cf. CCC 2290). The underlying premise of question you have asked is that humans may never do something that can cause harm to their bodies and has no compensating health value. There are, however, many human activities, not just smoking, that fall under that category but are not forbidden or sinful. Examples include drinking alcohol, riding motorcycles, boxing, and playing tackle football. All of these activities, when done without the requisite care and prudence, cause harm; some of them can cause harm even when requisite care and prudence are taken.
The Church does require that people take “reasonable care” to protect their lives and preserve their physical health (cf. CCC 2288), but it cautions that:
If morality requires respect for the life of the body, it does not make it an absolute value. It rejects a neo-pagan notion that tends to promote the cult of the body, to sacrifice everything for its sake (CCC 2289).
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