Which environmental factor can lead to changes in skin coloration?

The correct answer relates to the various ways in which different environmental factors can influence skin coloration. In particular, smoking is known to contribute to changes in skin appearance over time. The chemicals in tobacco smoke can lead to a decrease in blood flow to the skin, resulting in a duller complexion and contributing to uneven skin tone. Additionally, smoking can damage collagen and elastin, which are essential for maintaining skin structure and elasticity, ultimately affecting skin color and leading to signs of premature aging.

While exposure to sunlight is a significant factor (as it causes tanning and sunspots), the specific context of smoking directly impacts skin health and coloration because of its harmful effects on blood circulation and skin integrity. Pollution can also affect the skin by causing irritation or inflammatory responses, but it does not as directly relate to changes in coloration as a result of lifestyle choices like smoking. Allergies might cause temporary changes in skin coloration due to reactions, but they are generally not a chronic factor influencing long-term skin tone alterations.