Every year, World No Tobacco Day highlights different dimensions of the global tobacco epidemic. The 2026 campaign focuses on “unmasking the appeal” of tobacco and nicotine products, drawing attention to how flavours, vaping devices, glossy packaging, and digital marketing are used to attract younger users.Yet modern science suggests that addiction is not shaped by marketing and behaviour alone. Researchers increasingly believe that some individuals may be biologically more vulnerable to nicotine dependence than others. Two adolescents may experiment with cigarettes in the same classroom. One may never touch tobacco again. The other may spend decades trapped in dependence. The difference may not be explained solely by the environment. Part of it may already be embedded in the brain’s circuitry. Dopamine circuit Nicotine is the principal addictive component of tobacco. Once inhaled, nicotine enters the bloodstream and reaches the brain within seconds. There, it binds to nicotinic acetylcholine receptors–specialised receptors involved in nerve cell communication and triggers the release of dopamine. Dopamine is often simplistically described as a “pleasure chemical,” but its role is far more sophisticated. It is central to the brain’s reward-learning system. Dopamine teaches the brain to repeat behaviours associated with reward, comfort, novelty, or survival. This is what makes nicotine extraordinarily difficult to escape. Gradually, the brain begins associating tobacco use with morning tea, workplace breaks, loneliness, stress relief, social gatherings, or emotional regulation. Over time, nicotine use often shifts from reward-seeking to relief from withdrawal. Repeated nicotine exposure also remodels the brain itself. The brain’s reward system gradually becomes less responsive, forcing the individual to consume greater amounts of nicotine to achieve the same effect. Tolerance, dependence, irritability, and withdrawal begin to emerge in sequence. Health toll Tobacco injures nearly every organ system in the body. It damages the heart, blood vessels, lungs, and multiple other organs, and is strongly linked to cancers involving the lung, oral cavity, pancreas, bladder, and several other tissues. In India alone, tobacco contributes to more than a million deaths annually. Yet, despite decades of awareness campaigns and graphic warnings, tobacco use persists across societies. This persistence pushed scientists toward a more uncomfortable question. Why do some individuals become dependent far more rapidly than others, despite similar exposure? Genetic signals The search for answers led researchers into the field of behavioural genetics. Twin studies provided some of the earliest clues. Identical twins often showed striking similarities in smoking behaviour even when raised in different environments. This suggested that inherited biological factors were influencing vulnerability to addiction. Twin and family studies have shown that there is not one specific gene that determines who will develop a smoking addiction, but rather several genes that make an individual susceptible to being addicted to nicotine. One of the most important discoveries involved a cluster of genes, CHRNA5, CHRNA3, and CHRNB4, on chromosome 15. These genes help construct the very receptors through which nicotine acts inside the brain. More recent studies suggest that many nicotinic receptor systems in the brain may contribute to nicotine dependence, rather than a single receptor pathway alone. Certain variants within these genes appear to alter how nicotine is experienced. Some individuals may feel less unpleasant during early tobacco use, increasing the likelihood of repeated use and eventual dependence. Another important gene, CYP2A6, influences how rapidly the body metabolises nicotine. Individuals who break down nicotine quickly may consume more frequently to maintain nicotine levels. Others process nicotine slowly and may smoke less intensely. Modern genomic studies have shown that addiction is not governed by a single “smoking gene.” Instead, it emerges from hundreds of small genetic influences interacting with environmental factors, stress, personality, social exposure, and opportunity. Family echoes Tobacco addiction is polygenic and probabilistic rather than deterministic. Genes may increase susceptibility, but they do not guarantee addiction. Environmental influences continue to play a decisive role. Peer groups, childhood exposure, stress, advertising, availability, and cultural acceptance all shape whether a biologically vulnerable individual eventually develops dependence. Scientists often summarise this interaction through a simple idea: genes may create vulnerability, but the environment influences expression. Engineered addiction Tobacco companies understood the addictive power of nicotine long before the public fully appreciated it. Tobacco manufacturers carefully manipulated nicotine delivery, smoke chemistry, flavouring, and product design to maximise dependence.. Modern nicotine products have become increasingly sophisticated, using chemistry and flavouring to make initiation easier among adolescents. Flavoured products further reduce aversion and increase experimentation among young users. The “appeal” of tobacco, therefore, is not accidental. It is deliberately engineered. Beyond morality The genetics of tobacco addiction do not mean addiction is inevitable. Millions quit successfully every year. Yet the science does challenge the older moralistic belief that addiction represents nothing more than a failure of character. Some brains inherit vulnerability to nicotine. Some individuals may experience stronger cravings, more severe withdrawal symptoms, or greater difficulty quitting because of inherited differences in brain chemistry and nicotine metabolism. Understanding this shifts the conversation away from blame and toward treatment. Addiction is not simply a bad habit. It is a chronic, relapsing, biologically rooted public health disorder. The cigarette may rest between the fingers, but addiction ultimately resides within the architecture of the brain. (Dr. C. Aravinda is an academic and public health physician. The views expressed are personal. aravindaaiimsjr10@hotmail.com; Veera Rajagopal, physician-scientist, Chief Scientific Officer at Wellytics, working on human genetics, population health, and drug discovery in India,veera.scientist@gmail.com)