Smoking causes oxygen deficiency in the body because of :

Smoking causes oxygen deficiency primarily due to the inhalation of carbon monoxide (CO), a poisonous gas found in tobacco smoke [t2]. Hemoglobin in human blood normally has a high affinity for oxygen [c1]. However, carbon monoxide has a significantly higher affinity for hemoglobin than oxygen does, leading it to bind preferentially and form carboxyhemoglobin [t8]. This process effectively replaces oxygen in the red blood cells, reducing the blood's oxygen-carrying capacity and preventing vital organs from receiving sufficient oxygen [t2][t9]. While smoking also involves carbon dioxide (CO2), CO2 is naturally transported in dissolved form in plasma and does not compete for hemoglobin binding sites in the same disruptive manner as CO [c1][c4]. Therefore, the specific mechanism for the acute oxygen deficiency (hypoxia) observed in smokers is the increase in CO content in the blood [t4][t7].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Do You Know? > p. 90
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.7 > p. 91
3. [3] https://www.betterhealth.vic.gov.au/health/healthyliving/smoking-effects-on-your-body
4. [4] https://www.sciencedirect.com/science/article/pii/S0006497120751438
5. [5] https://discovery.ucl.ac.uk/id/eprint/10143032/1/Ke-Ting%20Pan_10143032_Thesis_sigs_removed.pdf