Which environmental factor is known to affect skin tone negatively?

Smoking is recognized as a significant environmental factor that negatively affects skin tone. It leads to poor circulation, reduced oxygen supply, and cumulative damage at a cellular level. The toxins in cigarette smoke can cause oxidative stress, contributing to the breakdown of collagen and elastin, which are essential for maintaining healthy, youthful skin. This degradation can lead to a dull complexion, uneven skin tone, and an increase in skin issues like wrinkles and dryness.

In addition to these effects, smoking can further exacerbate conditions such as hyperpigmentation and contribute to a sallow appearance. The combination of these factors results in a noticeable impact on skin tone over time, making smoking one of the most detrimental habits for maintaining healthy skin.

In contrast, while exposure to sunlight is also harmful due to UV radiation's potential to damage skin and cause discoloration, it is not the only factor to consider as its effects can be managed with proper sun protection. High humidity can have both positive and negative effects on skin hydration, and cold temperatures may lead to dryness but don't have the same direct impact on skin tone as smoking.