Ultra-violet Light

UV light activates the pigment melanin in the skin, and thereby creates a tan.
UVA penetrates deep into the dermis were it can cause premature ageing and the formation of free-radicals.  These molecules disrupt production of collagen and elastin, the fibres that give the skin its strength and elasticity.  Reduced elasticity leads to wrinkling.  Dilated capillaries are often present on a sun-damaged skin. UVB causes thickening of the stratum corneum layer and is the main ray involved in hyper pigmentation as it only penetrates into the epidermis.

Cold Climate

When the skin is exposed to the cold, less sebum is produced.  This could cause the skin’s barrier to become impaired, allowing moisture to evaporate.

Hot Climate

In very hot weather more moisture is lost as perspiration: perspiration increases, to cool the skin and regulate the body's temperature. 
More sebum is produced in warm weather.

Humidity

Moisture loss from the skin is also affected by the humidity (water content) of the surrounding air.  In hot, dry weather humidity will be slow, so water loss will be high; e.g. the skin would be more dehydrated in the presence of air conditioning and central heating.

Extreme Temperatures

Alternating heat and cold often leads to the formation of broken capillaries and could cause the skin to become sensitised.

Incorrect or Poor Skin Care

Harsh alkaline chemicals such as detergents, soaps and alcohol base products remove sebum from the skin's surface and destroy the acid mantle.  The skin will have less protection against the environment.  Constant rubbing and pulling of the skin can also weaken the collagen fibres, resulting in wrinkling of the skin.
Mannerism such as tugging, pulling, or pushing the facial muscles should also be avoided, as it can contribute to premature wrinkling.

Pollution

Environmental pollutants such as lead, mercury and aluminium can accumulate in the body.  One result is the formation of dangerous chemicals that attack proteins in the cells.  Such pollutants find their way into food through polluted waters, rain and dust.  To protect the body, always wash vegetables thoroughly and eat a diet rich in vitamins C and E.
Air pollution, involving carbon from smoke, chemical discharges from factories, and fumes from car exhausts, should be removed from the skin by effective cleansing.  If not cleansed thoroughly, it can lead to congestion and breakouts.  Absorption of these pollutants is reduced by the application of moisturiser that will form a barrier over the skin surface.  Absorbed pollutants can lead to skin sensitivity and allergic reactions.