Harm reduction is the principle that it is often inappropriate to just demand that people forgo an activity because it entails risks, and therefore it is wise to reduce the risks instead. Typically it is used to refer to activities that some people consider “immoral” and thus are inclined to demand that they just cease – such as sexual activity (where condoms serve as harm reduction) or injection drug use (where providing clean needles serves as harm reduction). But this principle applies to activities without such stigma as well. For example, motorized transport is quite dangerous, but society does not tell people to avoid it (not even for “unnecessary” travel); rather, we provide seatbelts and other safety features and try to make the roads safe. For stigmatized behaviors, the justification for harm reduction often includes the observation that even if one wants to end the activity, it is not going to happen, so better to make it less harmful (e.g., teenagers are going to have sex, so better that they use condoms).
Tobacco harm reduction applies these principles to tobacco use. In particular, it encourages people who are going to use tobacco to not smoke (which is extremely hazardous) but to use low-risk alternatives instead. Most smoke-free tobacco/nicotine products, including smokeless tobacco, e-cigarettes, and NRT (pharmaceutical nicotine) are roughly 99% less harmful than smoking, and many would-be smokers find one or more of them to be a good alternative to smoking. It must be stressed just how great the harm reduction is with THR. Other attempts to reduce harm by offering lower-risk forms of the behavior (ie. seat belts, bike helmets) reduce the risk by 10% or 50%, whereas THR comes very close to eliminating the risks entirely.