a) Nicotine stimulates and upregulates growth and branching of blood vessels (via upregulation of vascular growth factor), especially of capillaries, which improves the nutrient delivery and cleanup (antioxidant & detox enzyme supplies) to all tissues, including brain and skin (provided person's intake of nutrients and supplements is adequate).
b) Tobacco smoke (not nicotine) upregulates production of glutathione, catalase and SOD (our body's chief internal antioxidant and detox enzymes, sometimes used in cosmetics for skin rejuvenation), to nearly double levels.
c) Carbon monoxide in low concentration (as delivered in tobacco smoke) acts as a signaling mechanism in human biochemical networks to increase blood circulation, oxygenation and reduce inflammation.
d) Nitric oxide in low concentrations (as provided by tobacco smoke) acts as neurotransmitter, signaling to cardiovascular system to increase blood supplies to peripheral tissues (this is the biochemical mechanism behind the Viagra effect).
e) Tobacco smoke upregulates levels of "youth hormones" DHEA and testosterone and reduces their decline with age.
f) The highest quality brands (Japanese) of the miracle skin supplement and rejuvenator, Conezyme Q10 are produced from tobacco leaf, which is still the best source of natural Co-Q10 (since it includes the full synergistic complex which the cheaper synthetic production methods cannot replicate).
g) Deprenyl (selegiline), which mimics the selective MAO B inhibitory properties of tobacco smoke (this is not related to nicotine) and is used in smoking cessation "therapies" for that reason, has become quite popular in life-extension circles, due to its almost magical rejuvenating powers.
h) Nicotinic acid (byproduct of oxidized nicotine, as in burning tobacco, delivered directly into arterial bloodstream), along with its salts and various organic compounds, are skin-protective agents, used in cosmetic and pharmaceutical industry.