Extreme temperatures, and the speed of change between them, impact on skin health.
In cold conditions skin reacts by narrowing the blood vessels to protect the body from losing too much heat. Sustained cold temperatures reduce sebaceous gland secretion and cause skin to dry out. Read more in dry skin.
In hot and humid conditions (for example tropical countries or a sauna) sweat glands produce more sweat, leaving the skin moist and shiny and, in some cases, prone to acne.
Low humidity, as found in aeroplane cabins and even caused by central heating, can cause skin to become dehydrated and lead to increased sensitivity.
Some skin conditions, for example rosacea, can also be triggered by hot temperatures. This is one of the reasons why it is recommended to use warm rather than hot water for facial cleansing, hand washing and bathing.