Premature Aging
Research shows that there are, in fact, two distinct types of aging. Aging caused by the genes we inherit is called intrinsic (internal) aging. The other type of aging is known as extrinsic (external) aging and is caused by environmental factors, such as exposure to the sun’s rays.

Any actions that produce free radical activities in the skin, will increase the speed of skin aging, as has been explained in the previous pages in this section. Unprotected sun exposure causes damage to the skin's components and generates free radicals that promote secondary skin damage. Smoking produces free radicals in the body and skin which results in the damage we call aging. Pollution in the air can have a similar affect upon the skin by producing free radicals that cause damage. These are concepts that most people are familiar with.
Some skin care products contain free radicals and the use of products with these ingredients actually promotes skin aging.

Intrinsic aging, also known as the natural aging process, is a continuous process that normally begins in our mid-20s. Within the skin, collagen production slows, and elastin, the substance that enables skin to snap back into place, has a bit less spring. Dead skin cells do not shed as quickly and turnover of new skin cells may decrease slightly. While these changes usually begin in our 20s, the signs of intrinsic aging are typically not visible for decades

A number of extrinsic, or external, factors often act together with the normal aging process to prematurely age our skin. Most premature aging is caused by sun exposure. Other external factors that prematurely age our skin are repetitive facial expressions, gravity, sleeping positions, and smoking.