The main cause behind why the skin looks yellow, dull and rough is because of glycation and carbonylation.
Besides age, other external factors such as UV, pollution and stress etc also has a huge effect on the stratum corneum. People with sensitive and dry skin are easily irritated by external stimuli and hence, they need to pay extra attention to their skin.
When glycation and carbonylation occur in keratin fibers, this will cause dryness and aged skin
Mechanism Illustrated! - The mechanism of glycation and carbonylation