There are more causes of facial darkening, such as.
Sun exposure, dust contamination (e.g. soot, coal dust, soot, etc.), which may cause darkening of the face.
Changes in environmental temperature, such as walking from a warm room to a cold outdoor area, or a change in season, a sudden change to cold, from a warm area to a cold area, may cause a darkening of the face.
Some people have poor health, or are undernourished, which can also lead to a darker complexion if they are tired or sleep deprived.
Emotional changes, especially in people with darker complexions.
Drastic changes in mood such as anger, disappointment, shame, upset or fright can cause a person to darken their face.
Blood-related disorders such as anaemia, low blood pressure and low blood sugar often lead to a darker complexion as well.
Diseases of the heart and liver and kidneys can also cause a darker face.