Does your body odour change as you get older?
Yes, your body odour changes noticeably with age: from your forties onwards your skin produces a compound that adds a greasy, grassy note, and at the same time you become less able to perceive smells yourself.
From your forties onwards, your body odour contains a compound that is completely absent in younger people: 2-nonenal. This is a waste product formed when certain fatty acids in the outermost layer of your skin slowly oxidise. It has a greasy, grassy smell that is perceived as unpleasant. In test subjects between the ages of 26 and 39, 2-nonenal was not detected at all; from age 40 onwards it was, and the amount continues to rise with age.
The mechanism is reasonably well understood. As we age, the quantity of certain unsaturated fatty acids on the skin surface increases, as do the oxidation products released in the process. That combination leads to the formation of 2-nonenal. This has not only been demonstrated in laboratory research, but positive associations have also been found between the concentrations of those fatty acids, the oxidation products, and 2-nonenal in people themselves.
A study focused on developing new measurement techniques names four other volatile compounds as potential age indicators in body odour. However, that finding is still in its early stages: it was not the primary aim of that research, and for now you cannot draw many firm conclusions from it.
There is another factor to consider: as you age, you also perceive smells less well yourself. Both sensitivity to odours and the ability to identify them decline, even when measured over a period of five years. Older people also notice this themselves. This means that a change in odour that others can detect may be less readily noticed by yourself.
Two studies (PMID 11286617, 37447706) support the presence of 2-nonenal in people over 40 with reasonable evidence and a plausible mechanism. One study (PMID 35956746) on measurement techniques names four additional compounds, but the evidence for these is limited. The decline in sense of smell with age is strongly supported by a population study with 5 years of follow-up (PMID 41065093).
Does your skin get thicker or thinner as you age?
Your skin thins at two levels with age: that is well established. Retinoid creams have the most support if you want to slow that process; discuss stronger variants (such as tretinoin) with your doctor or dermatologist.
Does chronically poor air quality age your skin?
Chronic exposure to air pollution measurably accelerates skin ageing, and the evidence for this is reasonably consistent. If you live or work in a structurally polluted environment, paying extra attention to your skin barrier (a good moisturiser, sun protection) is a worthwhile step.
Does smoking age a smoker's skin on the inside too, or only on the outside?
Smoking does not only age the outside of your skin; it damages blood vessels, protective barriers and inflammatory regulation from the inside out. Quitting helps, but some damage, such as atherosclerosis, remains visible for decades.
What do smoking and alcohol do to the ageing of your skin?
Smoking demonstrably accelerates skin ageing through oxidative stress and inflammation. There are indications for alcohol, but the evidence is too thin for firm conclusions.
Does your skin age faster than your organs?
It has not been proven that skin as an organ naturally ages faster than your internal organs, but it is more vulnerable to sun and other external stimuli that measurably raise biological age. Limiting UV exposure is the best-supported way to slow skin ageing.
Does urban pollution accelerate the ageing of your skin?
Urban pollution probably accelerates skin ageing, primarily through increased pigmentation spots and a weakened skin barrier. The combination with sun exposure is the most harmful, so good sun protection is the most concrete step you can take right now.