Phytochemicals regulate plant and ecosystem interactions, playing key roles helping in pathogen to withstand abiotic stresses like atmospheric pollutants. Plant defence metabolites come from primary and secondary metabolic pathways, including phenylpropanoid, isoprenoid, and alkaloid routes. Antibiotic compounds in plants are either preformed (phytoanticipins) or inducible (phytoalexins). Phytoanticipins include saponins, cyanogenic glycosides, glucosinolates, and polyamines. Polyamines, such as putrescine, spermidine, and spermine, are plant growth regulators present in all plant species. They play pivotal roles in maturation, blooming, other developmental phenomenon, and stress response by stabilizing cellular elements and protecting biomolecules from free radicals. Polyamines enhance stress tolerance, helping plants cope with negative effects dually on abiotic and biotic stresses, like environmental stressors, fungal, bacterial, viral infections, and insect attacks. The anti-stress properties of polyamines are evident in their impact on physiological parameters, photosynthetic pigments, and reduction of stress markers and antioxidants. Recent research focuses on the potential of exogenous polyamine application to augment plant tolerance to several abiotic stresses, nutrient scarcity, salinity, drought, metal toxicity, temperature extremes, UV irradiation, ozone, air pollutants, and herbicides. Additionally, the interplay between ethylene and polyamines at the level of S-adenosylmethionine may influence their biosynthesis and plant phenotype.