When we refer to skin tone we mean the luminosity and evenness of your complexion. Change of tone is associated with premature skin ageing and is exasperated by lifestyle factors such as smoking, poor diet and alcohol consumption as well as dehydration and exposure to the sun.
As we age our skin becomes more "dull" and loses the "glow" and "luminosity" of youth. Contributing factors to change of skin tone include smoking, drinking alcohol, bad diet, sun damage and skin dehydration.
When we talk about change of tone it is usually in reference to the skin on the face.
Change of tone is part of the natural ageing process but women may find it more noticeable, as their skin is different to men's. Smokers, heavy drinkers, people with poor diet and those who spend too much time in the sun are more likely to age prematurely and, as a result, more likely to see changes in their skin tone.